Fix some overlap mismatch

This was caught by the following test:

```

int main(void) {
    char c[32];
    memcpy(c, c + 16, 16);
}
```

Reported-by: q66

1 files changed, 11 insertions, 0 deletions

diff --git a/tests/test_issue57.c b/tests/test_issue57.c
new file mode 100644
index 0000000..ee9c38e
--- /dev/null
+++ b/tests/test_issue57.c
@@ -0,0 +1,11 @@
+#include "common.h"
+
+#include <string.h>
+
+int main(int argc, char** argv) {
+  char buffer[32];
+  memcpy(buffer , buffer + 16, 16);
+  puts(buffer);
+
+  return ret;
+}