ANDROID: Fix NPE android issue

Author: chrisws

src/platform/android/app/src/main/java/net/sourceforge/smallbasic/MainActivity.java

@@ -792,7 +792,7 @@ private String getExternalStorage() {
     } else if (android.os.Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
       // https://commonsware.com/blog/2019/06/07/death-external-storage-end-saga.html
       File[] dirs = getExternalMediaDirs();
-      result = dirs[0].getAbsolutePath();
+      result = dirs != null && dirs.length > 0 ? dirs[0].getAbsolutePath() : getInternalStorage();
     } else {
       result = getInternalStorage();
     }

src/platform/android/jni/display.cpp

@@ -86,7 +86,7 @@ void Canvas::fillRect(int left, int top, int width, int height, pixel_t drawColo
         break;
       } else if (posY >= dtY) {
         pixel_t *line = getLine(posY);
-        for (int x = 0; x < width; x++) {
+        for (int x = 0; x < width && line; x++) {
           int posX = x + left;
           if (posX == _w) {
             break;