Keep a non-ASCII last letter in the server browser's tag name

tag_text dropped a trailing lead byte even when its character was whole, so
"Skate Café" was listed as "Skate Caf". The browser shows the tag name until
the server answers a query, so hosts without a forwarded query port kept it.

Extension/Multiplayer/Test/protocol_tests.cpp

@@ -856,6 +856,17 @@ void dedicated_server_codec() {
     check(row && row->dedicated && row->name == "Big  friendly server" && row->map == ad.map && row->players == 3 &&
               row->capacity == 16 && row->password_required && row->code == format_invite({server, ad.secret}),
           "Server tags did not round trip");
+    // A whole last character is kept, and one the byte limit cuts through is dropped whole.
+    const auto accented = read_server_tags(dingosdk::server::server_tags({"Skate Caf\xC3\xA9", "Caf\xC3\xA9", 1, 8, false, true, 1}), server);
+    check(accented && accented->name == "Skate Caf\xC3\xA9" && accented->map == "Caf\xC3\xA9",
+          "A server name lost its non-ASCII last letter");
+    for (std::size_t lead = 0; lead < 3; ++lead) {
+        std::string euros(lead, 'a');
+        for (int i = 0; i < 50; ++i) euros += "\xE2\x82\xAC";
+        const auto cut = dingosdk::server::server_tags({euros, "Caf\xC3\xA9", 1, 8, false, true, 1});
+        const auto name = cut.substr(cut.find(",n") + 2);
+        check(cut.size() < 128 && name.size() > lead && (name.size() - lead) % 3 == 0, "A server name was cut inside a character");
+    }
     check(!read_server_tags(tags, player), "A player's ID read as a server");
     check(!read_server_tags("reskate,v1,k1,c4", server), "An incompatible server version listed");
 }

Server/steam_server.cpp

@@ -1,4 +1,5 @@
 #include "steam_server.h"
+#include "server_text.h"
 #include "Extension/Multiplayer/Net/protocol.h"
 #ifdef _WIN32
 #include <Windows.h>
@@ -12,6 +13,7 @@
 #include <thread>
 #include <unistd.h>
 #endif
+#include <algorithm>
 #include <cstdio>
 #include <cstring>
 #include <optional>
@@ -45,14 +47,11 @@ struct SteamIP {
 // Tags are comma separated, so a name loses its commas; the whole list must
 // stay under Steam's 128 byte limit.
 std::string tag_text(std::string_view text, std::size_t limit) {
-    std::string result;
-    for (const char c : text) {
-        if (result.size() >= limit) break;
-        result += c == ',' ? ' ' : c;
-    }
-    // Never end inside a UTF-8 sequence.
-    while (!result.empty() && (static_cast<unsigned char>(result.back()) & 0xC0) == 0x80) result.pop_back();
-    if (!result.empty() && (static_cast<unsigned char>(result.back()) & 0xC0) == 0xC0) result.pop_back();
+    std::string result(text);
+    std::replace(result.begin(), result.end(), ',', ' ');
+    // Cut at the limit only, and never through a character: a whole last character
+    // is kept ("Café" stays "Café"), one the limit splits is dropped.
+    cut_text(result, limit);
     return result;
 }
 // Steam's library prints its own crash-reporting notes ("Setting breakpad