Fix NPE when IMM#invalidateInput() is called too early

This is a follow up CL to my previous CL [1], which introduced

  InputMethodManager#invalidateInput(View).

One thing I overlooked is that apps may call that API even before

  InputMethodManager#mCurrentInputMethodSession,

which results in a NullPointerException.

With this CL, such a case will be gracefully fallen back into

  InputMethodManager#restartInput(View)

like other cases when IMM#invalidateInput() is not available.

 [1]: I3161755779080f98bcef0e47dd0c5247d8a3a256
      daa6695c2e

Fix: 213350732
Test: atest CtsInputMethodTestCases:InputMethodStartInputLifecycleTest
Change-Id: I67458494b3069498a1395e3278f6a975e821e610

core/java/android/view/inputmethod/InputMethodManager.java

@@ -2031,14 +2031,20 @@ public final class InputMethodManager {
      * @param inputConnection the connection to be invalidated.
      * @param textSnapshot {@link TextSnapshot} to be used to update {@link EditorInfo}.
      * @param sessionId the session ID to be sent.
+     * @return {@code true} if the operation is done. {@code false} if the caller needs to fall back
+     *         to {@link InputMethodManager#restartInput(View)}.
      * @hide
      */
-    public void doInvalidateInput(@NonNull RemoteInputConnectionImpl inputConnection,
+    public boolean doInvalidateInput(@NonNull RemoteInputConnectionImpl inputConnection,
             @NonNull TextSnapshot textSnapshot, int sessionId) {
         synchronized (mH) {
             if (mServedInputConnection != inputConnection || mCurrentTextBoxAttribute == null) {
                 // OK to ignore because the calling InputConnection is already abandoned.
-                return;
+                return true;
+            }
+            if (mCurrentInputMethodSession == null) {
+                // IME is not yet bound to the client.  Need to fall back to the restartInput().
+                return false;
             }
             final EditorInfo editorInfo = mCurrentTextBoxAttribute.createCopyInternal();
             editorInfo.initialSelStart = mCursorSelStart = textSnapshot.getSelectionStart();
@@ -2051,6 +2057,7 @@ public final class InputMethodManager {
                     sessionId);
             forAccessibilitySessions(wrapper -> wrapper.invalidateInput(editorInfo,
                     mServedInputConnection, sessionId));
+            return true;
         }
     }
 

core/java/com/android/internal/inputmethod/RemoteInputConnectionImpl.java

@@ -282,9 +282,8 @@ public final class RemoteInputConnectionImpl extends IInputContext.Stub {
 
                     if (!alwaysTrueEndBatchEditDetected) {
                         final TextSnapshot textSnapshot = ic.takeSnapshot();
-                        if (textSnapshot != null) {
-                            mParentInputMethodManager.doInvalidateInput(this, textSnapshot,
-                                    nextSessionId);
+                        if (textSnapshot != null && mParentInputMethodManager.doInvalidateInput(
+                                this, textSnapshot, nextSessionId)) {
                             return;
                         }
                     }