Check Meta before Toggling Conversion Factor (#12237)

If it has been customized so as to set the conversion factor to read only, `toggle_conversion_factor` should respect that setting.
diff --git a/erpnext/public/js/controllers/transaction.js b/erpnext/public/js/controllers/transaction.js
index 1814061..1452ce7 100644
--- a/erpnext/public/js/controllers/transaction.js
+++ b/erpnext/public/js/controllers/transaction.js
@@ -693,7 +693,7 @@
 		// toggle read only property for conversion factor field if the uom and stock uom are same
 		if(this.frm.get_field('items').grid.fields_map.conversion_factor) {
 			this.frm.fields_dict.items.grid.toggle_enable("conversion_factor",
-				(item.uom != item.stock_uom)? true: false);
+				((item.uom != item.stock_uom) && !frappe.meta.get_docfield(cur_frm.fields_dict.items.grid.doctype, "conversion_factor").read_only)? true: false);
 		}
 
 	},