GSDX: Avoid crash when TBW == 0

plugins/GSdx/GSTextureCache.cpp

@@ -435,7 +435,7 @@ GSTextureCache::Target* GSTextureCache::LookupTarget(const GIFRegTEX0& TEX0, int
 		// From a performance point of view, it might cost a little on big upscaling
 		// but normally few RT are miss so it must remain reasonable.
 		if (s_IS_OPENGL) {
-			if (m_preload_frame) {
+			if (m_preload_frame && TEX0.TBW > 0) {
 				GL_INS("Preloading the RT DATA");
 				// RT doesn't have height but if we use a too big value, we will read outside of the GS memory.
 				int page0 = TEX0.TBP0 >> 5;