Prevent divide by 0 exception and cleanup

It seems a check was missed, since we initialize lineHeight to 0...

this fixes arduino/Arduino#7861

Author: Vipas-ana

src/main/java/org/fife/ui/rsyntaxtextarea/SyntaxView.java

@@ -946,11 +946,12 @@ else if (y > alloc.y + alloc.height) {
 		else {
 
 			Element map = doc.getDefaultRootElement();
+			lineHeight = host!=null ? host.getLineHeight() : lineHeight;
 			int lineIndex = Math.abs((y - alloc.y) / lineHeight);//metrics.getHeight() );
-FoldManager fm = host.getFoldManager();
-//System.out.print("--- " + lineIndex);
-lineIndex += fm.getHiddenLineCountAbove(lineIndex, true);
-//System.out.println(" => " + lineIndex);
+			FoldManager fm = host.getFoldManager();
+			//System.out.print("--- " + lineIndex);
+			lineIndex += fm.getHiddenLineCountAbove(lineIndex, true);
+			//System.out.println(" => " + lineIndex);
 			if (lineIndex >= map.getElementCount()) {
 				return host.getLastVisibleOffset();
 			}
@@ -1019,4 +1020,4 @@ public int yForLineContaining(Rectangle alloc, int offs)
 	}
 
 
-}
+}