meta: Compute correct buffer size with SkipRows/SkipPixels

meta: Compute correct buffer size with SkipRows/SkipPixels

If the user is specifying a subregion of a buffer using SKIP_ROWS and
SKIP_PIXELS, we must compute the buffer size carefully as the end of the
last row may be much shorter than stride*image_height*depth. The current
code tries to memcpy from beyond the end of the user data, for example
causing:

==28136== Invalid read of size 8
==28136==    at 0x4C2D94E: memcpy@@GLIBC_2.14 (vg_replace_strmem.c:915)
==28136==    by 0xB4ADFE3: brw_bo_write (brw_batch.c:1856)
==28136==    by 0xB5B3531: brw_buffer_data (intel_buffer_objects.c:208)
==28136==    by 0xB0F6275: _mesa_buffer_data (bufferobj.c:1600)
==28136==    by 0xB0F6346: _mesa_BufferData (bufferobj.c:1631)
==28136==    by 0xB37A1EE: create_texture_for_pbo (meta_tex_subimage.c:103)
==28136==    by 0xB37A467: _mesa_meta_pbo_TexSubImage (meta_tex_subimage.c:176)
==28136==    by 0xB5C8D61: intelTexSubImage (intel_tex_subimage.c:195)
==28136==    by 0xB254AB4: _mesa_texture_sub_image (teximage.c:3654)
==28136==    by 0xB254C9F: texsubimage (teximage.c:3712)
==28136==    by 0xB2550E9: _mesa_TexSubImage2D (teximage.c:3853)
==28136==    by 0x401CA0: UploadTexSubImage2D (teximage.c:171)
==28136==  Address 0xd8bfbe0 is 0 bytes after a block of size 1,024 alloc'd
==28136==    at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==28136==    by 0x402014: PerfDraw (teximage.c:270)
==28136==    by 0x402648: Draw (glmain.c:182)
==28136==    by 0x8385E63: ??? (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x83896C8: fgEnumWindows (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x838641C: glutMainLoopEvent (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x8386C1C: glutMainLoop (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x4019C1: main (glmain.c:262)
==28136==
==28136== Invalid read of size 8
==28136==    at 0x4C2D940: memcpy@@GLIBC_2.14 (vg_replace_strmem.c:915)
==28136==    by 0xB4ADFE3: brw_bo_write (brw_batch.c:1856)
==28136==    by 0xB5B3531: brw_buffer_data (intel_buffer_objects.c:208)
==28136==    by 0xB0F6275: _mesa_buffer_data (bufferobj.c:1600)
==28136==    by 0xB0F6346: _mesa_BufferData (bufferobj.c:1631)
==28136==    by 0xB37A1EE: create_texture_for_pbo (meta_tex_subimage.c:103)
==28136==    by 0xB37A467: _mesa_meta_pbo_TexSubImage (meta_tex_subimage.c:176)
==28136==    by 0xB5C8D61: intelTexSubImage (intel_tex_subimage.c:195)
==28136==    by 0xB254AB4: _mesa_texture_sub_image (teximage.c:3654)
==28136==    by 0xB254C9F: texsubimage (teximage.c:3712)
==28136==    by 0xB2550E9: _mesa_TexSubImage2D (teximage.c:3853)
==28136==    by 0x401CA0: UploadTexSubImage2D (teximage.c:171)
==28136==  Address 0xd8bfbe8 is 8 bytes after a block of size 1,024 alloc'd
==28136==    at 0x4C28C20: malloc (vg_replace_malloc.c:296)
==28136==    by 0x402014: PerfDraw (teximage.c:270)
==28136==    by 0x402648: Draw (glmain.c:182)
==28136==    by 0x8385E63: ??? (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x83896C8: fgEnumWindows (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x838641C: glutMainLoopEvent (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x8386C1C: glutMainLoop (in /usr/lib/x86_64-linux-gnu/libglut.so.3.9.0)
==28136==    by 0x4019C1: main (glmain.c:262)
==28136==

Fixes regression from commit 7f396189f073d626c5f7a2c232dac92b65f5a23f
Author: Jason Ekstrand <jason.ekstrand@intel.com>
Date:   Mon Jan 5 18:17:04 2015 -0800

    meta: Add a BlitFramebuffers-based implementation of TexSubImage

v2: However, the teximage we create does need to be width x full_height x 1

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jason Ekstrand <jason.ekstrand@intel.com>
Cc: Neil Roberts <neil@linux.intel.com>
Reviewed-by Neil Roberts <neil@linux.intel.com>