Add NPE check to SoftButtonCapabilities onCapabilityRetrieved

Author: Julian Kast

base/src/main/java/com/smartdevicelink/managers/screen/BaseSoftButtonManager.java

@@ -136,7 +136,11 @@ public void onCapabilityRetrieved(Object capability) {
                     for (WindowCapability windowCapability : mainDisplay.getWindowCapabilities()) {
                         int currentWindowID = windowCapability.getWindowID() != null ? windowCapability.getWindowID() : PredefinedWindows.DEFAULT_WINDOW.getValue();
                         if (currentWindowID == PredefinedWindows.DEFAULT_WINDOW.getValue()) {
-                            softButtonCapabilities = windowCapability.getSoftButtonCapabilities().get(0);
+                            if (windowCapability.getSoftButtonCapabilities() != null) {
+                                softButtonCapabilities = windowCapability.getSoftButtonCapabilities().get(0);
+                            } else {
+                                softButtonCapabilities = null;
+                            }
                             break;
                         }
                     }