mesa: remove redundant NULL check

This can never be NULL in any of the entry paths.

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>

src/mesa/main/teximage.c

@@ -2504,6 +2504,8 @@ copytexsubimage_error_check(struct gl_context *ctx, GLuint dimensions,
                             GLint xoffset, GLint yoffset, GLint zoffset,
                             GLint width, GLint height, const char *caller)
 {
+   assert(texObj);
+
    struct gl_texture_image *texImage;
 
    /* Check that the source buffer is complete */
@@ -2530,12 +2532,6 @@ copytexsubimage_error_check(struct gl_context *ctx, GLuint dimensions,
       return GL_TRUE;
    }
 
-   /* Get dest image pointers */
-   if (!texObj) {
-      _mesa_error(ctx, GL_OUT_OF_MEMORY, "%s()", caller);
-      return GL_TRUE;
-   }
-
    texImage = _mesa_select_tex_image(texObj, target, level);
    if (!texImage) {
       /* destination image does not exist */