Don't rely on unsequenced evaluation order in bintool/metadata.h (ras…

…pberrypi#187) (raspberrypi#188)

metadata.h:258:44: warning: multiple unsequenced modifications to 'i' [-Wunsequenced]

Fix this warning by reading the low and high words in order, then combining them,
rather than doing so in a single expression.

bintool/metadata.h

@@ -255,7 +255,9 @@ struct partition_table_item : public single_byte_size_item {
             new_p.flags = permissions_flags & (~PICOBIN_PARTITION_PERMISSIONS_BITS);
 
             if (new_p.flags & PICOBIN_PARTITION_FLAGS_HAS_ID_BITS) {
-                new_p.id = (uint64_t)data[i++] | ((uint64_t)data[i++] << 32);
+                uint32_t low = data[i++];
+                uint32_t high = data[i++];
+                new_p.id = (uint64_t)low | ((uint64_t)high << 32);
             }
 
             uint8_t num_extra_families = (new_p.flags & PICOBIN_PARTITION_FLAGS_ACCEPTS_NUM_EXTRA_FAMILIES_BITS) >> PICOBIN_PARTITION_FLAGS_ACCEPTS_NUM_EXTRA_FAMILIES_LSB;