tdf#91641 adjust cursor when deleting preceding characters

IMDeleteSurrounding is used by input methods to take multiple
keystrokes and convert them into a special character.  Then the
composing keystrokes are removed.
Before this fix, the cursor placement was not adjusted,
so the special character was inserted in the wrong position
and if 3+ keystrokes were involved, the wrong characters were deleted.

Change-Id: I35b97bc150dc68ffe65eebc59450e21e0033bd16
Reviewed-on: https://gerrit.libreoffice.org/15961Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

vcl/unx/gtk/window/gtksalframe.cxx

@@ -4655,7 +4655,7 @@ gboolean GtkSalFrame::IMHandler::signalIMDeleteSurrounding( GtkIMContext*, gint
     uno::Reference<accessibility::XAccessibleEditableText> xText = lcl_GetxText(pFocusWin);
     if (xText.is())
     {
-        sal_uInt32 nPosition = xText->getCaretPosition();
+        sal_Int32 nPosition = xText->getCaretPosition();
         // #i111768# range checking
         sal_Int32 nDeletePos = nPosition + offset;
         sal_Int32 nDeleteEnd = nDeletePos + nchars;
@@ -4667,6 +4667,14 @@ gboolean GtkSalFrame::IMHandler::signalIMDeleteSurrounding( GtkIMContext*, gint
             nDeleteEnd = xText->getCharacterCount();
 
         xText->deleteText(nDeletePos, nDeleteEnd);
+        //tdf91641 adjust cursor if deleted chars shift it forward (normal case)
+        if (nDeletePos < nPosition)
+        {
+            if (nDeleteEnd <= nPosition)
+                xText->setCaretPosition( nPosition-(nDeleteEnd-nDeletePos) );
+            else
+                xText->setCaretPosition( nDeletePos );
+        }
         return true;
     }