prompt: mouse clicks that moved the cursor need no further processing

This fixes https://savannah.gnu.org/bugs/?48917.

src/prompt.c

@@ -69,7 +69,7 @@ int do_statusbar_input(bool *ran_func, bool *finished,
 	if (do_statusbar_mouse() == 1)
 	    input = get_kbinput(bottomwin);
 	else
-	    input = ERR;
+	    return ERR;
     }
 #endif