clean up zero-byte logfile on immediate exit

Otherwise, a zero-byte log file stays behind after every call to `i3
--get-socketpath`. Also, replace "return" calls with more explicit "exit"
calls.

Before:

$ ls -ld /tmp/i3* | wc -l; \
  repeat 10 i3 --get-socketpath >/dev/null; \
  ls -ld /tmp/i3* | wc -l
1
11

Now:

$ ls -ld /tmp/i3* | wc -l; \
  repeat 10 i3 --get-socketpath >/dev/null; \
  ls -ld /tmp/i3* | wc -l
1
1

Signed-off-by: Julius Plenz <julius@plenz.com>

src/main.c

@@ -343,10 +343,10 @@ int main(int argc, char *argv[]) {
                     char *socket_path = root_atom_contents("I3_SOCKET_PATH");
                     if (socket_path) {
                         printf("%s\n", socket_path);
-                        return 0;
+                        exit(EXIT_SUCCESS);
                     }
 
-                    return 1;
+                    exit(EXIT_FAILURE);
                 } else if (strcmp(long_options[option_index].name, "shmlog-size") == 0 ||
                            strcmp(long_options[option_index].name, "shmlog_size") == 0) {
                     shmlog_size = atoi(optarg);