Reset struct alignment back to standard after each #pragma pack (n)

When using #pragma pack (n) to change the alignment for a struct
to n bytes, it is necessary to reset the alignment to the standard
value as otherwise the changed alignment is used throughout the
whole program code which causes other structs to become unaligned.

gpt.h

@@ -57,6 +57,7 @@ struct GPTHeader {
    uint32_t partitionEntriesCRC;
    unsigned char reserved2[GPT_RESERVED];
 }; // struct GPTHeader
+#pragma pack ()
 
 // Data in GPT format
 class GPTData {