glsl2: check for _NumLinkedShaders being 0

Otherwise spring 0.82+.4.0 crashes when starting a game
because prog->_LinkedShaders[0] is NULL.

This also fixes piglit test cases glsl-link-empty-prog-0[12].

diff --git a/src/glsl/linker.cpp b/src/glsl/linker.cpp
index e0823c3af420136213f420263f0e98742d0b27e0..02c7c29878365e49d113128e5b973ab1a5b916e7 100644 (file)
--- a/src/glsl/linker.cpp
+++ b/src/glsl/linker.cpp
@@ -1476,7 +1476,7 @@ link_shaders(GLcontext *ctx, struct gl_shader_program *prog)
 
    assign_uniform_locations(prog);
 
-   if (prog->_LinkedShaders[0]->Type == GL_VERTEX_SHADER) {
+   if (prog->_NumLinkedShaders && prog->_LinkedShaders[0]->Type == GL_VERTEX_SHADER) {
       /* FINISHME: The value of the max_attribute_index parameter is
        * FINISHME: implementation dependent based on the value of
        * FINISHME: GL_MAX_VERTEX_ATTRIBS.  GL_MAX_VERTEX_ATTRIBS must be