Revert "mesa: Remove pointless comparison of unsigned integer with a negative constant."

This reverts commit a05fdbcb719ac64e6be842372813f0f4ca2f4f93.

Removing the comparison is wrong. The comparison with -1 should be changed
to another value (probably PROGRAM_UNDEFINED) along with another
change in the shader assembler.

Conflicts:

	src/mesa/shader/prog_execute.c
1 file changed