Fix regression in handling of procedural cosmetic filters

Related commit:
- gorhill@91caed3

Related issue:
- uBlockOrigin/uBlock-issues#2185 (comment)

src/js/cosmetic-filtering.js

@@ -828,7 +828,8 @@ FilterContainer.prototype.cssRuleFromProcedural = function(json) {
     if ( pfilter.cssable !== true ) { return; }
     const { tasks, action } = pfilter;
     let mq;
-    if ( tasks !== undefined && tasks.length === 1 ) {
+    if ( tasks !== undefined ) {
+        if ( tasks.length > 1 ) { return; }
         if ( tasks[0][0] !== ':matches-media' ) { return; }
         mq = tasks[0][1];
     }

src/js/static-filtering-parser.js

@@ -1862,9 +1862,6 @@ Parser.prototype.SelectorCompiler = class {
         }
 
         const out = { selector: prefix };
-        if ( root && this.sheetSelectable(prefix) ) {
-            out.cssable = true;
-        }
 
         if ( tasks.length !== 0 ) {
             out.tasks = tasks;
@@ -1875,6 +1872,19 @@ Parser.prototype.SelectorCompiler = class {
             out.action = action;
         }
 
+        // Flag to quickly find out whether the filter can be converted into
+        // a declarative CSS rule.
+        if (
+            root &&
+            (action === undefined || action[0] === ':style') &&
+            (
+                tasks.length === 0 ||
+                tasks.length === 1 && tasks[0][0] === ':matches-media'
+            )
+        ) {
+            out.cssable = this.sheetSelectable(prefix);
+        }
+
         return out;
     }