Remove elision of leading wildcard in some filter patterns

Related issue:
- https://github.com/uBlockOrigin/uBlock-issues/issues/882

Related commits:
- https://github.com/gorhill/uBlock/commit/a95ef16e064a
- https://github.com/gorhill/uBlock/commit/7971b223855d

Leading wildcards before valid token characters need to
be kept in order to respect the semantic of the filter.
A leading wildcard in such case changes the semantic of
a filter, i.e. two following filters are semantically
different:

    example/abc
    *example/abc

As a result, µBlock.BidiTrieContainer.indexOf() is now
able to deal with a needle of length zero -- which is
what happens in FilterPatternLeft(Ex) with filter
patterns starting with `*` (or `^*`) and followed by
valid token characters (0-9, a-z and %).

src/js/static-net-filtering.js

@@ -616,6 +616,9 @@ const FilterPatternPlainX = class extends FilterPatternPlain {
 
 /******************************************************************************/
 
+// https://github.com/gorhill/uBlock/commit/7971b223855d#commitcomment-37077525
+//   Mind that the left part may be empty.
+
 const FilterPatternLeft = class {
     constructor(i, n) {
         this.i = i | 0;
@@ -633,8 +636,10 @@ const FilterPatternLeft = class {
     }
 
     logData(details) {
+        details.pattern.unshift('*');
+        if ( this.n === 0 ) { return; }
         const s = bidiTrie.extractString(this.i, this.n);
-        details.pattern.unshift(s, '*');
+        details.pattern.unshift(s);
         details.regex.unshift(restrFromPlainPattern(s), '.*');
     }
 
@@ -2529,16 +2534,8 @@ const FilterParser = class {
         this.tokenBeg = matches.index;
 
         // https://www.reddit.com/r/uBlockOrigin/comments/dpcvfx/
-        //   Since we found a valid token, we can get rid of leading/trailing
+        //   Since we found a valid token, we can get rid of trailing
         //   wildcards if any.
-        // https://github.com/gorhill/uBlock/commit/7971b223855d#commitcomment-37077525
-        //   Mind that changing the pattern may change token start index.
-        if ( this.firstWildcardPos === 0 ) {
-            this.f = this.f.slice(1);
-            this.firstWildcardPos = this.secondWildcardPos;
-            this.secondWildcardPos = -1;
-            this.tokenBeg -= 1;
-        }
         if ( this.firstWildcardPos !== -1 ) {
             const lastCharPos = this.f.length - 1;
             if ( this.firstWildcardPos === lastCharPos ) {

src/js/strie.js

@@ -636,6 +636,7 @@ const roundToPageSize = v => (v + PAGE_SIZE-1) & ~(PAGE_SIZE-1);
     // Find the left-most instance of substring in main string
     // WASMable.
     indexOf(haystackLeft, haystackEnd, needleLeft, needleLen) {
+        if ( needleLen === 0 ) { return haystackLeft; }
         haystackEnd -= needleLen;
         if ( haystackEnd < haystackLeft ) { return -1; }
         needleLeft += this.buf32[CHAR0_SLOT];

src/js/wasm/biditrie.wat

@@ -544,6 +544,10 @@
     (local $c0 i32)
     block $fail
     block $succeed
+    ;; if ( needleLen === 0 ) { return haystackLeft; }
+    get_local $needleLen
+    i32.eqz
+    br_if $succeed
     ;; haystackEnd -= needleLen;
     get_local $haystackEnd
     get_local $needleLen