Fix an issue where stale missing tag errors could persist when canceling drawing a new way (close #5918)

Don't show missing tags error for a feature that is still being drawn (re: #5898)

modules/validations/missing_tag.js

@@ -29,6 +29,14 @@ export function validationMissingTag() {
             return [];
         }
 
+        var mode = context.mode();
+        if (entity.type === 'way' && mode &&
+            (mode.id === 'draw-area' || (mode.id === 'draw-line' && !mode.isContinuing)) &&
+            mode.wayID === entity.id) {
+            // don't flag missing tag issues if drawing a new way
+            return [];
+        }
+
         var messageObj = {};
         var missingTagType;