Reset pendingCameraSwitch as false after failed to post switchCameraOnThread to camera thread.

BUG=webrtc:6981

Review-Url: https://codereview.webrtc.org/2625133007
Cr-Commit-Position: refs/heads/master@{#16105}
diff --git a/webrtc/sdk/android/api/org/webrtc/VideoCapturerAndroid.java b/webrtc/sdk/android/api/org/webrtc/VideoCapturerAndroid.java
index 45a5fcb..d002925 100644
--- a/webrtc/sdk/android/api/org/webrtc/VideoCapturerAndroid.java
+++ b/webrtc/sdk/android/api/org/webrtc/VideoCapturerAndroid.java
@@ -184,8 +184,13 @@
         }
       }
     });
-    if (!didPost && switchEventsHandler != null) {
-      switchEventsHandler.onCameraSwitchError("Camera is stopped.");
+    if (!didPost) {
+      synchronized (pendingCameraSwitchLock) {
+        pendingCameraSwitch = false;
+      }
+      if (switchEventsHandler != null) {
+        switchEventsHandler.onCameraSwitchError("Camera is stopped.");
+      }
     }
   }