Ensure line is unfolded when highlighting for error

Fixes arduino#8457

For some reason, getCurrentTab().getTextArea().getFoldManager().ensureOffsetNotInClosedFold(line) doesn't work here; there no documentation on what offset is.
Also, getFoldForLine(line) returns null even if the line is folded (bug in rsyntaxtextarea?)

Author: facchinm

app/src/processing/app/Editor.java

@@ -1648,6 +1648,13 @@ public void removeAllLineHighlights() {
   }
 
   public void addLineHighlight(int line) throws BadLocationException {
+    if (getCurrentTab().getTextArea().getFoldManager().isLineHidden(line)) {
+      for (int i = 0; i < getCurrentTab().getTextArea().getFoldManager().getFoldCount(); i++) {
+        if (getCurrentTab().getTextArea().getFoldManager().getFold(i).containsLine(line)) {
+          getCurrentTab().getTextArea().getFoldManager().getFold(i).setCollapsed(false);
+        }
+      }
+    }
     getCurrentTab().getTextArea().addLineHighlight(line, new Color(1, 0, 0, 0.2f));
     getCurrentTab().getTextArea().setCaretPosition(getCurrentTab().getTextArea().getLineStartOffset(line));
   }