Fix SFMDATA getting a terminator that it shouldn't get if NULL pointer is given (#290)

src/ines.cpp

@@ -1057,7 +1057,12 @@ static int iNES_Init(int num) {
 				}
 			}
 			if (head.ROM_type & 8)
+			{
+				if (ExtraNTARAM != NULL)
+				{
 					AddExState(ExtraNTARAM, 2048, 0, "EXNR");
+				}
+			}
 			tmp->init(&iNESCart);
 			return 0;
 		}

src/state.cpp

@@ -860,6 +860,9 @@ void ResetExState(void (*PreSave)(void), void (*PostSave)(void))
 
 void AddExState(void *v, uint32 s, int type, const char *desc)
 {
+	//do not accept extra state information if a null pointer was provided for v, so list won't terminate early
+	if (v == 0) return;
+	
 	if(s==~0)
 	{
 		SFORMAT* sf = (SFORMAT*)v;