Reject + sign in SplitHostPort

It is better to reject it with an error. For example,

$ bitcoin-cli -rpcconnect=127.0.0.1:+23501 -getinfo
error: Invalid port provided in -rpcconnect: 127.0.0.1:+23501

Author: MarcoFalke

src/util/strencodings.cpp

@@ -78,10 +78,9 @@ bool SplitHostPort(std::string_view in, uint16_t& portOut, std::string& hostOut)
     bool fBracketed = fHaveColon && (in[0] == '[' && in[colon - 1] == ']'); // if there is a colon, and in[0]=='[', colon is not 0, so in[colon-1] is safe
     bool fMultiColon{fHaveColon && colon != 0 && (in.find_last_of(':', colon - 1) != in.npos)};
     if (fHaveColon && (colon == 0 || fBracketed || !fMultiColon)) {
-        uint16_t n;
-        if (ParseUInt16(in.substr(colon + 1), &n)) {
+        if (const auto n{ToIntegral<uint16_t>(in.substr(colon + 1))}) {
             in = in.substr(0, colon);
-            portOut = n;
+            portOut = *n;
             valid = (portOut != 0);
         }
     } else {