regex: fix simple char match (#17701)

vlib/regex/regex_complex_test.v

@@ -0,0 +1,19 @@
+import regex
+
+fn test_complex_matching() {
+	tmp_text := r"[export:'something']
+const (
+some_const   = [1114111, 127, 2047, 65535, 1114111]!
+
+)
+
+[export:'something_empty']
+const (
+empty_const   = ()
+)
+"
+	query := r'\[export:\S+\]\sconst\s\(\s+\S+\s{3}=\s\('
+	mut re := regex.regex_opt(query) or { panic(err) }
+	mut a := re.find_all(tmp_text)
+	assert a == [86, 138]
+}