glx: Fix handling of property list received from the server in glXImportContextEXT

glx: Fix handling of property list received from the server in glXImportContextEXT

The primary problem was that the number of reply bytes read is clamped
to sizeof(propList), but the loop that processes the properties tries
to examine all of the properties sent by the server.  If the server
sends 47,000 properties, we only read 3 but process all 47,000.

NOTE: This is a candidate for the 7.11 branch.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Eric Anholt <eric@anholt.net>