SanitizeString: allow '(' and ')'

'(' and ')' are valid in user agent strings, so should be reported
as such in RPC `getpeerinfo`.

Fixes #4537.

src/utilstrencodings.cpp

@@ -16,7 +16,7 @@ using namespace std;
 
 // safeChars chosen to allow simple messages/URLs/email addresses, but avoid anything
 // even possibly remotely dangerous like & or >
-static string safeChars("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890 .,;_/:?@");
+static string safeChars("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890 .,;_/:?@()");
 string SanitizeString(const string& str)
 {
     string strResult;