Fixed a case in which the title was being truncated

When using multiple lines in the title, the text is being truncated at
the top due to the top margin being set to a negative margin.
Now only adding the margin when the value is not negative.

Author: alexkok

library/src/main/java/moe/feng/common/stepperview/VerticalStepperItemView.java

@@ -162,8 +162,12 @@ private void prepareViews(@NonNull Context context) {
 			@Override
 			public void onGlobalLayout() {
 				int singleLineHeight = mTitleText.getMeasuredHeight();
-				ViewGroup.MarginLayoutParams mlp = (MarginLayoutParams) mTitleText.getLayoutParams();
-				mlp.topMargin = (mPointFrame.getMeasuredHeight() - singleLineHeight) / 2;
+				int topMargin = (mPointFrame.getMeasuredHeight() - singleLineHeight) / 2;
+				// Only update top margin when it is positive, preventing titles being truncated.
+				if (topMargin > 0) {
+					ViewGroup.MarginLayoutParams mlp = (MarginLayoutParams) mTitleText.getLayoutParams();
+					mlp.topMargin = topMargin;
+				}
 			}
 		});
 	}