fix: prevent crash in prune command after loop exit

Added missing return statements after loop.exit() calls in the prune
command
to prevent function execution from continuing after exit is called. This
fixes a crash that occurred when the function continued executing code
after
requesting the event loop to exit, potentially accessing invalid memory.

Author: ice909

libs/linglong/src/linglong/cli/cli.cpp

@@ -1513,11 +1513,13 @@ int Cli::prune([[maybe_unused]] CLI::App *subcommand)
           if (!ret) {
               this->printer.printErr(ret.error());
               loop.exit(-1);
+              return;
           }
 
           if (!ret->packages) {
               this->printer.printErr(LINGLONG_ERRV("No packages to prune."));
               loop.exit(0);
+              return;
           }
 
           this->printer.printPruneResult(*ret->packages);