FileSys: split the constructor into an Open method, in order to notify the opener something went wrong.

Kernel: Return an invalid handle to OpenFile when it failed to open.

src/core/file_sys/file_sdmc.h

@@ -22,6 +22,12 @@ public:
     File_SDMC(const Archive_SDMC* archive, const std::string& path, const Mode mode);
     ~File_SDMC() override;
 
+    /**
+     * Open the file
+     * @return true if the file opened correctly
+     */
+    bool Open() override;
+
     /**
      * Read data from the file
      * @param offset Offset in bytes to start reading data from
@@ -61,6 +67,8 @@ public:
     bool Close() const override;
 
 private:
+    std::string path;
+    Mode mode;
     FileUtil::IOFile* file;
 };