Fix deallocation error in test.cpp

If a test command fails to execute, `expectedrom` and `truerom` will be
freed twice, which causes failure on Windows debug. The pointers are set
to null after freeing to reslolve this.

src/asar-tests/test.cpp

@@ -55,7 +55,9 @@
     {                           \
         numfailed++;            \
         free(expectedrom);      \
+        expectedrom = NULL;     \
         free(truerom);          \
+        truerom = NULL;         \
         printf("Failure!\n\n"); \
         continue;               \
     }