net: Have LookupNumeric return a CService directly

Also fix up a few small issues:
- Lookup with "badip:port" now sets the port to 0
- Don't allow assert to have side-effects

src/netbase.cpp

@@ -231,9 +231,14 @@ bool Lookup(const char *pszName, CService& addr, int portDefault, bool fAllowLoo
     return true;
 }
 
-bool LookupNumeric(const char *pszName, CService& addr, int portDefault)
+CService LookupNumeric(const char *pszName, int portDefault)
 {
-    return Lookup(pszName, addr, portDefault, false);
+    CService addr;
+    // "1.2:345" will fail to resolve the ip, but will still set the port.
+    // If the ip fails to resolve, re-init the result.
+    if(!Lookup(pszName, addr, portDefault, false))
+        addr = CService();
+    return addr;
 }
 
 struct timeval MillisToTimeval(int64_t nTimeout)