MAINT-6123 Fix for LLTextureCache::writeToFastCache crash

indra/newview/lltexturecache.cpp

@@ -1928,6 +1928,12 @@ bool LLTextureCache::writeToFastCache(S32 id, LLPointer<LLImageRaw> raw, S32 dis
 		{
 			//make a duplicate to keep the original raw image untouched.
 			raw = raw->duplicate();
+			if (raw->isBufferInvalid())
+			{
+				LL_WARNS() << "Invalid image duplicate buffer" << LL_ENDL;
+				return false;
+			}
+
 			raw->scale(w, h) ;
 			
 			discardlevel += i ;