CameraService: Check Thread::run for failed threads.

While a thread failing to launch is somewhat catastrophic, checking the
result and printing the error / returning early is good practice.

Test: Ran CameraThreadSafetyTest.
Change-Id: I8c1d3fe197ef8af631960dd286096287de9a280e
diff --git a/services/camera/libcameraservice/device3/Camera3OutputStream.cpp b/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
index 69163a5..e12d8be 100644
--- a/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
+++ b/services/camera/libcameraservice/device3/Camera3OutputStream.cpp
@@ -702,7 +702,8 @@
             mTotalBufferCount ++;
             res = mPreviewFrameSpacer->run(String8::format("PreviewSpacer-%d", mId).string());
             if (res != OK) {
-                ALOGE("%s: Unable to start preview spacer", __FUNCTION__);
+                ALOGE("%s: Unable to start preview spacer: %s (%d)", __FUNCTION__,
+                        strerror(-res), res);
                 return res;
             }
         }