strip entered IP addresses/hostname of whitespace before resolving

It is easy to accidentally paste whitespace along with the actual
connection information into the Play Network Game window's entry.
Fortunately it is also easy for us to handle this by removing that
whitespace before passing the string on.

src/gui/C4StartupNetDlg.cpp

@@ -956,7 +956,28 @@ bool C4StartupNetDlg::DoOK()
 		const char *szDirectJoinAddress = pJoinAddressEdt->GetText();
 		if (szDirectJoinAddress && *szDirectJoinAddress)
 			{
-			AddReferenceQuery(szDirectJoinAddress, C4StartupNetListEntry::NRQT_DirectJoin);
+			// First do some acrobatics to avoid trying to resolve addresses with leading
+			// or trailing whitespace, which is easily pasted in with an IP address.
+			// We can trivially skip whitespace at the beginning, but we need a copy to
+			// omit whitespace at the end.
+			while(std::isspace(*szDirectJoinAddress))
+				// skip whitespace at the beginning
+				++szDirectJoinAddress;
+			if(!*szDirectJoinAddress)
+				// entry empty, apart from whitespace
+				return true;
+			const char *szDirectJoinAddressEnd = szDirectJoinAddress + std::strlen(szDirectJoinAddress) - 1;
+			while(std::isspace(*szDirectJoinAddressEnd))
+				// skip whitespace at the end
+				--szDirectJoinAddressEnd;
+			if(*++szDirectJoinAddressEnd)
+				{
+				// Make a temporary copy of the part that is not trailing whitespace, if any
+				std::string strDirectJoinAddressStripped(szDirectJoinAddress, szDirectJoinAddressEnd - szDirectJoinAddress);
+				AddReferenceQuery(strDirectJoinAddressStripped.c_str(), C4StartupNetListEntry::NRQT_DirectJoin);
+				}
+			else
+				AddReferenceQuery(szDirectJoinAddress, C4StartupNetListEntry::NRQT_DirectJoin);
 			// Switch focus to list so another OK joins the specified address
 			SetFocus(pGameSelList, true);
 			return true;