extraneous mipmap generation prune

OR spits out quite a few pointless mips for non square textures, which can lead to it triggering that AssertFatal(mNumMipLevels <= c_maxMipLevels, "GBitmap::allocateBitmap: too many miplevels"); entry

Engine/source/gfx/gfxTextureManager.cpp

@@ -1098,7 +1098,7 @@ void GFXTextureManager::_validateTexParams( const U32 width, const U32 height,
                currHeight = 1;
 
             inOutNumMips++;
-         } while ( currWidth != 1 || currHeight != 1 );
+         } while ( currWidth != 1 && currHeight != 1 );
       }
    }
 }