Fix layout column problem when GF Styles Pro enabled

Move the grid CSS classes first in the class order, so that they aren't removed due to an mPDF processing bug when there are a lot of classes.

README.txt

@@ -109,6 +109,7 @@ Gravity PDF can be run on most modern shared web hosting without any issues. It
 
 = 6.8.1 =
 * Bug: Fix Form Editor saving problem for Gravity Forms v2.6.*
+* Bug: Fix Drag and Drop Column layout issue when the GF Styles Pro plugin is enabled
 
 = 6.8.0 =
 * Feature: Add PDF Download metabox to Gravity Flow Inbox for logged-in users with appropriate capability

src/Helper/Helper_Field_Container.php

@@ -299,7 +299,7 @@ protected function process_skipped_fields( GF_Field $field ) {
 	 * @since  4.0
 	 */
 	protected function strip_field_of_any_classmaps( GF_Field $field ) {
-		$field->cssClass = str_replace( array_keys( $this->class_map ), ' ', $field->cssClass );
+		$field->cssClass = trim( str_replace( array_keys( $this->class_map ), ' ', $field->cssClass ) );
 	}
 
 	/**

src/Helper/Helper_Field_Container_Gf25.php

@@ -61,7 +61,7 @@ public function generate( GF_Field $field ) {
 		parent::generate( $field );
 
 		if ( $this->get_field_width( $field ) < 100 && strpos( $field->cssClass, 'grid grid-' ) === false ) {
-			$field->cssClass .= ' grid grid-' . $field->layoutGridColumnSpan;
+			$field->cssClass = trim( 'grid grid-' . $field->layoutGridColumnSpan . ' ' . $field->cssClass );
 		}
 
 		/* Mark as the end of this row */