AI 145083: ADT #1777728: fix NPE when AVD list is empty

BUG=1777728

Automated import of CL 145083

tools/sdkmanager/libs/sdklib/src/com/android/sdklib/avd/AvdManager.java

@@ -742,7 +742,7 @@ public final class AvdManager {
     private void buildAvdList(ArrayList<AvdInfo> list) throws AndroidLocationException {
         
         File[] avds = buildAvdFilesList();
-
+        if (avds != null) {
             for (File avd : avds) {
                 AvdInfo info = parseAvdInfo(avd, false /*acceptError*/);
                 if (info != null) {
@@ -750,6 +750,7 @@ public final class AvdManager {
                 }
             }
         }
+    }
 
     /**
      * Computes the internal list of <em>not</em> available AVDs.