In CAP messages, handle the last arg as a list of capabilities

Instead of just one. This fixes the issue of the "trailing whitespace" since we
now split it on ' '

Fix #3442

src/irc/irc_client.cpp

@@ -1340,11 +1340,13 @@ long int IrcClient::get_throttle_limit() const
 void IrcClient::on_cap(const IrcMessage &message)
 {
   const auto& sub_command = message.arguments[1];
-  const auto& cap = message.arguments[2];
+  const auto& caps = utils::split(message.arguments[2], ' ', false);
+  for (const auto& cap: caps)
+    {
       auto it = this->capabilities.find(cap);
       if (it == this->capabilities.end())
         {
-      log_warning("Received a CAP message for something we didn’t ask, or that we already handled.");
+          log_warning("Received a CAP message for something we didn’t ask, or that we already handled: [", cap, "]");
           return;
         }
       Capability& capability = it->second;
@@ -1353,6 +1355,7 @@ void IrcClient::on_cap(const IrcMessage &message)
       else if (sub_command == "NACK")
         capability.on_nack();
       this->capabilities.erase(it);
+    }
   if (this->capabilities.empty())
     this->cap_end();
 }

tests/utils.cpp

@@ -28,6 +28,9 @@ TEST_CASE("String split")
   CHECK(splitted.size() == 2);
   CHECK(splitted[0] == "");
   CHECK(splitted[1] == "a");
+  splitted = utils::split("multi-prefix ", ' ');
+  CHECK(splitted[0] == "multi-prefix");
+  CHECK(splitted.size() == 1);
 }
 
 TEST_CASE("tolower")