Fix create flag handling in open (#3255)

If the create flag is specified, but the file already exists, then the file should open successfully, regardless of permissions.
This fixes a crash seen in Phantasy Star Online 2 New Genesis (CUSA29813)

src/core/libraries/kernel/file_system.cpp

@@ -118,6 +118,7 @@ s32 PS4_SYSV_ABI open(const char* raw_path, s32 flags, u16 mode) {
             return -1;
         }
 
+        if (!exists) {
             if (read_only) {
                 // Can't create files in a read only directory
                 h->DeleteHandle(handle);
@@ -126,6 +127,7 @@ s32 PS4_SYSV_ABI open(const char* raw_path, s32 flags, u16 mode) {
             }
             // Create a file if it doesn't exist
             Common::FS::IOFile out(file->m_host_name, Common::FS::FileAccessMode::Write);
+        }
     } else if (!exists) {
         // If we're not creating a file, and it doesn't exist, return ENOENT
         h->DeleteHandle(handle);