Russian: Set max_digits to 18

src/libespeak-ng/tr_languages.c

@@ -1638,4 +1638,5 @@ static void Translator_Russian(Translator *tr)
 
 	tr->langopts.numbers = NUM_DECIMAL_COMMA | NUM_OMIT_1_HUNDRED;
 	tr->langopts.numbers2 = NUM2_THOUSANDPLEX_VAR_THOUSANDS | NUM2_THOUSANDS_VAR1; // variant numbers before thousands
+	tr->langopts.max_digits = 18;
 }