Replace &vec[0] with vec.data()

When the vector is empty, using `&vec[0]` involves undefined behaviour. While that works fine most of the time, Flatpak builds aborted on a failed `__builtin_expect`.

I searched for such occurences across the codebase with the regex `(?<!&)&\w+\[0\]` and fixed those that would potentially cause issues.

src/core/loader/3dsx.cpp

@@ -342,7 +342,7 @@ ResultStatus AppLoader_THREEDSX::ReadIcon(std::vector<u8>& buffer) {
         file.Seek(hdr.smdh_offset, SEEK_SET);
         buffer.resize(hdr.smdh_size);
 
-        if (file.ReadBytes(&buffer[0], hdr.smdh_size) != hdr.smdh_size)
+        if (file.ReadBytes(buffer.data(), hdr.smdh_size) != hdr.smdh_size)
             return ResultStatus::Error;
 
         return ResultStatus::Success;