fix(steam): truncate presence to a valid UTF-8 sequence

With a host name such as "Êîðïîðàöèÿ Ìàéêðîñîôò; Âñå ïðàâà çàùèùåíû", we
will try to set a presence name like "test: Êîðïîðàöèÿ Ìàéêðîñîôò; Âñå
ïðàâà çàùèùåíû", assuming `steamname.txt` contains "test".

Steam, internally, truncates app names to fit in a 64-byte buffer with a
null terminator. However, the code which truncates does not ensure the
resulting UTF-8 sequence is valid, which might lead to the update being
rejected further down the line, which is especially likely with a name
consisting solely of multi-byte sequences, like the example name.

In this changeset, we circumvent this by truncating the name to 64 bytes
ourselves, and subsequently chopping off at the first invalid UTF-8
sequence.

code/components/steam/component.lua

@@ -0,0 +1,3 @@
+return function()
+	add_dependencies { "vendor:utfcpp" }
+end

code/components/steam/src/SteamComponent.cpp

@@ -19,6 +19,8 @@
 #include <sstream>
 #include <thread>
 
+#include <utf8.h>
+
 struct CfxPresenceState
 {
 	char gameName[512];
@@ -403,6 +405,17 @@ void SteamComponent::InitializePresence()
 			productName += fmt::sprintf(": %s", gameData->gameName);
 		}
 
+		// Steam requires the name to fit in a 64-byte buffer, so we try to make sure there's no unfinished UTF-8 sequences in that case
+		if (productName.length() >= 64)
+		{
+			productName = productName.substr(0, 63);
+
+			if (auto invalidPos = utf8::find_invalid(productName); invalidPos != std::string::npos)
+			{
+				productName = productName.substr(0, invalidPos);
+			}
+		}
+
 		// set our pipe appid
 		InterfaceMapper steamUtils(m_clientEngine->GetIClientUtils(m_steamPipe, "CLIENTUTILS_INTERFACE_VERSION001"));