LibCrypto: Reset cached trimmed length after add_into_accumulator

The trimmed cache length of the `UnsignedBigInteger` was not reset after
an `add_into_accumulator_without_allocation` operation because the
function manipulates the words directly.

This meant that if the trimmed length was calculated before this
operation it would be wrong after.

Libraries/LibCrypto/BigInt/Algorithms/SimpleOperations.cpp

@@ -66,6 +66,8 @@ void UnsignedBigIntegerAlgorithms::add_into_accumulator_without_allocation(Unsig
         // Note : The accumulator couldn't add the carry directly, so we reached its end
         accumulator.m_words.append(last_carry_for_word);
     }
+
+    accumulator.m_cached_trimmed_length = {};
 }
 
 /**