SNEAKY BUGFIX race condition between UI thread and CPU thread on disk insertion

- Previously we would start the CPU thread and then insert, which has been a long standing race condition, but
      possibly better exposed since the recent disk.c rephactor to use mmap I/O
    - This directly manifested on a Kindle Fire 1st Gen as a crash, and, anecdotally on other devices as a "stalled"
      disk read requiring a reboot of the virtual machine.  Yay for crappy devices helping to expose crappy code! (git
      blame me). =P

Android/app/src/main/java/org/deadc0de/apple2ix/Apple2DisksMenu.java

@@ -615,8 +615,6 @@ public class Apple2DisksMenu implements Apple2MenuView {
                 builder.setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
                     @Override
                     public void onClick(DialogInterface dialog, int which) {
-                        dialog.dismiss();
-                        mActivity.dismissAllMenus();
                         boolean isDriveA = diskA.isChecked();
                         boolean diskReadOnly = readOnly.isChecked();
                         if (isDriveA) {
@@ -626,6 +624,8 @@ public class Apple2DisksMenu implements Apple2MenuView {
                             Apple2Preferences.CURRENT_DISK_B_RO.saveBoolean(mActivity, diskReadOnly);
                             Apple2Preferences.CURRENT_DISK_B.saveString(mActivity, imageName);
                         }
+                        dialog.dismiss();
+                        mActivity.dismissAllMenus();
                     }
                 });
 

Android/jni/jnihooks.c

@@ -311,6 +311,8 @@ void Java_org_deadc0de_apple2ix_Apple2Activity_nativeChooseDisk(JNIEnv *env, job
     int drive = driveA ? 0 : 1;
     int ro = readOnly ? 1 : 0;
 
+    assert(cpu_isPaused() && "considered dangerous to insert disk image when CPU thread is running");
+
     LOG(": (%s, %s, %s)", path, driveA ? "drive A" : "drive B", readOnly ? "read only" : "read/write");
     if (disk6_insert(drive, path, ro)) {
         char *gzPath = NULL;