test-char: fix undefined behavior

Fixes the following failure with --enable-debug:

/tmp/qemu-test/src/tests/test-char.c:838:10: runtime error: load of value 40, which is not a valid value for type bool
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /tmp/qemu-test/src/tests/test-char.c:838:10 in
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

tests/test-char.c

@@ -745,7 +745,7 @@ static void char_socket_server_test(gconstpointer opaque)
     Visitor *v;
     QemuThread thread;
     int ret;
-    bool reconnected;
+    bool reconnected = false;
     char *optstr;
     QemuOpts *opts;