Return -1 from GetLineLength() if line number is out of range

Make wxTextCtrl behaviour in all ports consistent with the documentation
and also update wxStyledTextCtrl to behave accordingly.

Closes #18431.

src/msw/textctrl.cpp

@@ -1803,6 +1803,9 @@ int wxTextCtrl::GetLineLength(long lineNo) const
 {
     long pos = XYToPosition(0, lineNo);
 
+    if ( pos == -1 )
+        return -1;
+
     return GetLengthOfLineContainingPos(pos);
 }