mesa: reduce gl_array_object::VertexAttrib[] array from 32 to 16 elements

This array was mistakenly dimensioned with VERT_ATTRIB_MAX (32) but it
should really be MAX_VERTEX_GENERIC_ATTRIBS (16).

The generic vertex attributes are in addition to the conventional arrays
(except in NV vertex program mode- they alias/overlay in that case) so
the total of all conventional attributes plus generic attributes should
total 32 (not 48).

src/mesa/main/mtypes.h

@@ -1574,8 +1574,13 @@ struct gl_array_object
    struct gl_client_array PointSize;
    /*@}*/
 
-   /** Generic arrays for vertex programs/shaders */
-   struct gl_client_array VertexAttrib[VERT_ATTRIB_MAX];
+   /**
+    * Generic arrays for vertex programs/shaders.
+    * For NV vertex programs, these attributes alias and take priority
+    * over the conventional attribs above.  For ARB vertex programs and
+    * GLSL vertex shaders, these attributes are separate.
+    */
+   struct gl_client_array VertexAttrib[MAX_VERTEX_GENERIC_ATTRIBS];
 
    /** Mask of _NEW_ARRAY_* values indicating which arrays are enabled */
    GLbitfield _Enabled;