replace assertion with conditional in utilSafeFree()

src/util.h

@@ -148,8 +148,10 @@ utilAllocateCStr(const char* str, u32 max_len)
 void
 utilSafeFree(void* p)
 {
-	assert(p != nullptr);
-	free(p);
+	if (p)
+		free(p);
+	else
+		printf("%s(), free called on nullptr\n", __FUNCTION__);
 }
 
 #endif