Check if file was opened successfuly

src/main.c

@@ -14,6 +14,10 @@ int main(int argc, char *argv[]) {
 		return 1;
 	}
 	file = fopen(argv[1],"r");
+	if (file == NULL) {
+		fprintf(stderr,"Unable to open file.\n");
+		return 1;
+	}
 	struct SyntaxElement* code = parse(file);
 	fclose(file);
 	if (code == NULL) {