mesa: remove unneeded free() call in texstore_rgba()

The pointer will always be NULL since that's what we just tested for.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>

src/mesa/main/texstore.c

@@ -764,7 +764,6 @@ texstore_rgba(TEXSTORE_PARAMS)
       tempRGBA = malloc(4 * elementCount * sizeof(float));
       if (!tempRGBA) {
          free(tempImage);
-         free(tempRGBA);
          return GL_FALSE;
       }