mesa: handle numSamples=0 in _mesa_test_proxy_teximage()

Should fix the regressions reported in bug 96949.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96949
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/main/teximage.c

@@ -1271,8 +1271,6 @@ _mesa_test_proxy_teximage(struct gl_context *ctx, GLenum target,
 {
    uint64_t bytes, mbytes;
 
-   assert(numSamples > 0);
-
    if (numLevels > 0) {
       /* Compute total memory for a whole mipmap.  This is the path
        * taken for glTexStorage(GL_PROXY_TEXTURE_x).
@@ -1306,7 +1304,7 @@ _mesa_test_proxy_teximage(struct gl_context *ctx, GLenum target,
    }
 
    bytes *= _mesa_num_tex_faces(target);
-   bytes *= numSamples;
+   bytes *= MAX2(1, numSamples);
 
    mbytes = bytes / (1024 * 1024); /* convert to MB */