Consider an empty pattern with anchors to be dubious

Related issue:
- https://github.com/ryanbr/fanboy-adblock/issues/1384

src/js/codemirror/ubo-static-filtering.js

@@ -252,16 +252,16 @@ CodeMirror.defineMode('ubo-static-filtering', function() {
         if ( parser.category === parser.CATComment ) {
             return colorCommentSpan(stream);
         }
-        if ( (parser.slices[parserSlot] & parser.BITIgnore) !== 0 ) {
-            stream.pos += parser.slices[parserSlot+2];
-            parserSlot += 3;
-            return 'comment';
-        }
         if ( (parser.slices[parserSlot] & parser.BITError) !== 0 ) {
             stream.pos += parser.slices[parserSlot+2];
             parserSlot += 3;
             return 'error';
         }
+        if ( (parser.slices[parserSlot] & parser.BITIgnore) !== 0 ) {
+            stream.pos += parser.slices[parserSlot+2];
+            parserSlot += 3;
+            return 'comment';
+        }
         if ( parser.category === parser.CATStaticExtFilter ) {
             return colorExtSpan(stream);
         }

src/js/static-filtering-parser.js

@@ -636,7 +636,11 @@ const Parser = class {
                 this.toASCII(true) === false
             )
         ) {
-            this.markSpan(this.patternSpan, BITError);
+            this.markSlices(
+                this.patternLeftAnchorSpan.i,
+                this.optionsAnchorSpan.i,
+                BITError
+            );
         }
         this.netOptionsIterator.init();
     }
@@ -908,12 +912,17 @@ const Parser = class {
     // Examples of dubious filter content:
     //   - Spaces characters
     //   - Single character other than `*` wildcard
+    //   - Zero-length pattern with anchors
+    //     https://github.com/ryanbr/fanboy-adblock/issues/1384
     patternIsDubious() {
         return hasBits(this.patternBits, BITSpace) || (
             this.patternBits !== BITAsterisk &&
-            this.optionsSpan.len === 0 &&
+            this.optionsSpan.len === 0 && (
+                this.patternSpan.len === 0 &&
+                    this.patternLeftAnchorSpan.len !== 0 ||
                 this.patternSpan.len === 3 &&
                     this.slices[this.patternSpan.i+2] === 1
+            )
         );
     }