gl-renderer: Test for GL_EXT_unpack_subimage not GL_UNPACK_ROW_LENGTH

It is defined by the mesa #include, which is just a copy of the official
Khronos header.  It's just defined in a different section than the
extension tokens.  In the mean time, the extension tokens were renamed
to add a _EXT suffix (eg GL_UNPACK_ROW_LENGTH -> GL_UNPACK_ROW_LENGTH_EXT)
and we silently failed to used the subimage extension.
1 file changed