Don’t give a scary error about not being able to run on Android if there’s no...

Don’t give a scary error about not being able to run on Android if there’s no Android device connected.

packages/flutter_tools/lib/src/device.dart

@@ -230,13 +230,15 @@ class AndroidDevice extends _Device {
     _adbPath = _getAdbPath();
     _hasAdb = _checkForAdb();
 
-    // Checking for lollipop only needs to be done if we are starting an
-    // app, but it has an important side effect, which is to discard any
-    // progress messages if the adb server is restarted.
-    _hasValidAndroid = _checkForLollipopOrLater();
-
-    if (!_hasAdb || !_hasValidAndroid) {
-      _logging.severe('Unable to run on Android.');
+    if (isConnected()) {
+      // Checking for lollipop only needs to be done if we are starting an
+      // app, but it has an important side effect, which is to discard any
+      // progress messages if the adb server is restarted.
+      _hasValidAndroid = _checkForLollipopOrLater();
+
+      if (!_hasAdb || !_hasValidAndroid) {
+        _logging.severe('Unable to run on Android.');
+      }
     }
   }