Use safe UTF-8 path construction

runtime/include/runtime_config.h

@@ -777,7 +777,7 @@ inline std::string DvdRoot(std::string fallback = "") {
 inline std::filesystem::path ResolveRelativeTo(const std::filesystem::path& base,
                                                const std::string& value) {
     // Config strings are UTF-8; the char overload would decode via the ANSI codepage.
-    std::filesystem::path path(reinterpret_cast<const char8_t*>(value.c_str()));
+    std::filesystem::path path(std::u8string(value.begin(), value.end()));
     if (path.is_relative()) {
         path = base / path;
     }

runtime/src/hle/storage/riivolution.cpp

@@ -90,7 +90,7 @@ std::string RiivoGenericText(const fs::path& path) {
 }
 
 fs::path RiivoPathFromUtf8(const std::string& text) {
-    return fs::path(reinterpret_cast<const char8_t*>(text.c_str()));
+    return fs::path(std::u8string(text.begin(), text.end()));
 }
 
 std::string RiivoComparablePath(const fs::path& path) {