qga: unlink just created guest-file if fchmod() or fdopen() fails on it

We shouldn't allow guest filesystem pollution on error paths.
Suggested-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

qga/commands-posix.c

@@ -355,6 +355,9 @@ safe_open_or_create(const char *path, const char *mode, Error **err)
             }
 
             close(fd);
+            if (oflag & O_CREAT) {
+                unlink(path);
+            }
         }
     }