make sure the camera is not null when setting up the preview after measuring

app/src/main/kotlin/com/simplemobiletools/camera/Preview.kt

@@ -462,12 +462,14 @@ class Preview : ViewGroup, SurfaceHolder.Callback, MediaScannerConnection.OnScan
             }
 
             if (mSetupPreviewAfterMeasure) {
+                if (mCamera != null) {
                     mSetupPreviewAfterMeasure = false
-                mCamera?.stopPreview()
+                    mCamera!!.stopPreview()
                     setupPreview()
                 }
             }
         }
+    }
 
     fun enableFlash() {
         mParameters!!.flashMode = Camera.Parameters.FLASH_MODE_TORCH