gpu: keep the old signal strategy for null pointer

previous commits changes the behaviour of interrupt when meeting invalid params. Regresses to the same behaviour as before
needs more hwtest

src/core/hw/gpu.cpp

@@ -416,11 +416,15 @@ inline void Write(u32 addr, const T data) {
             LOG_TRACE(HW_GPU, "MemoryFill from 0x%08x to 0x%08x", config.GetStartAddress(),
                       config.GetEndAddress());
 
+            // It seems that it won't signal interrupt if "address_start" is zero.
+            // TODO: hwtest this
+            if (config.GetStartAddress() != 0) {
                 if (!is_second_filler) {
                     GSP_GPU::SignalInterrupt(GSP_GPU::InterruptId::PSC0);
                 } else {
                     GSP_GPU::SignalInterrupt(GSP_GPU::InterruptId::PSC1);
                 }
+            }
 
             // Reset "trigger" flag and set the "finish" flag
             // NOTE: This was confirmed to happen on hardware even if "address_start" is zero.