Prevent evaluating the SNFE until fully loaded

Related issue:
uBlockOrigin/uBlock-issues#2925

src/js/static-net-filtering.js

@@ -4123,6 +4123,8 @@ FilterContainer.prototype.reset = function() {
  this.optimizeTaskId = undefined;
  }
 
+ this.notReady = false;
+
  // Runtime registers
  this.$catBits = 0;
  this.$tokenHash = 0;
@@ -4215,6 +4217,8 @@ FilterContainer.prototype.freeze = function() {
  this.goodFilters.clear();
  filterArgsToUnit.clear();
 
+ this.notReady = false;
+
  // Optimizing is not critical for the static network filtering engine to
  // work properly, so defer this until later to allow for reduced delay to
  // readiness when no valid selfie is available.
@@ -4723,6 +4727,8 @@ FilterContainer.prototype.fromSelfie = async function(storage, path) {
 
  this.reset();
 
+ this.notReady = true;
+
  const results = await Promise.all([
  storage.get(`${path}/main`),
  storage.get(`${path}/destHNTrieContainer`).then(details =>
@@ -4767,6 +4773,14 @@ FilterContainer.prototype.fromSelfie = async function(storage, path) {
  this.bitsToBucketIndices = selfie.bitsToBucketIndices;
  bucketsFromSelfie(selfie.buckets);
  urlTokenizer.fromSelfie(selfie.urlTokenizer);
+
+ // If this point is never reached, it means the internal state is
+ // unreliable, and the caller is then responsible for resetting the
+ // engine and populate properly, in which case the `notReady` barrier
+ // will be properly reset.
+
+ this.notReady = false;
+
  return true;
 };
 
@@ -4811,6 +4825,8 @@ FilterContainer.prototype.matchAndFetchModifiers = function(
  fctxt,
  modifierName
 ) {
+ if ( this.notReady ) { return; }
+
  const typeBits = typeNameToTypeValue[fctxt.type] || otherTypeBitValue;
 
  $requestURL = urlTokenizer.setURL(fctxt.url);
@@ -4988,6 +5004,8 @@ FilterContainer.prototype.realmMatchString = function(
  typeBits,
  partyBits
 ) {
+ if ( this.notReady ) { return false; }
+
  const exactType = typeBits & 0x80000000;
  typeBits &= 0x7FFFFFFF;