Fix --appimage-mount mountpoint communication

Right now, the buffering of stdout prevents proper reading of the
mountpoint from stdout in scripts and other processes in general.

This commit fixes the runtime's behavior.

Author: TheAssassin

src/runtime.c

@@ -868,13 +868,23 @@ int main(int argc, char *argv[]) {
         }
         real_argv[i] = NULL;
 
-        if(arg && strcmp(arg,"appimage-mount")==0) {
+        if(arg && strcmp(arg, "appimage-mount") == 0) {
             char real_mount_dir[PATH_MAX];
-            if (realpath(mount_dir, real_mount_dir) == real_mount_dir)
+
+            if (realpath(mount_dir, real_mount_dir) == real_mount_dir) {
                 printf("%s\n", real_mount_dir);
-            else
+            } else {
                 printf("%s\n", mount_dir);
+            }
+
+            // stdout is, by default, buffered (unlike stderr), therefore in order to allow other processes to read
+            // the path from stdout, we need to flush the buffers now
+            // this is a less-invasive alternative to setbuf(stdout, NULL);
+            fflush(stdout);
+
             for (;;) pause();
+
+            exit(0);
         }
 
         /* Setting some environment variables that the app "inside" might use */