Fix memory corruption (too small IPC::Message::messageData)

[dwrobel]

Copying wpe_input_axis_event to IPC::Message::messageData
in the code like:

memcpy( message.messageData, &event, sizeof(event) );

causes memory corruption as the size of messageData is 24
while the size of wpe_input_axis_event is 28 bytes.

Dump of relevant offsets:

(gdb) ptype /o IPC::Message
/* offset | size / type = struct IPC::Message {
static const size_t size;
static const size_t dataSize;
/ 0 | 8 / uint64_t messageCode;
/ 8 | 24 */ uint8_t messageData[24];

                       /* total size (bytes):   32 */
                     }

(gdb) ptype /o wpe_input_axis_event
/* offset | size / type = struct wpe_input_axis_event {
/ 0 | 4 / enum wpe_input_axis_event_type type;
/ 4 | 4 / uint32_t time;
/ 8 | 4 / int x;
/ 12 | 4 / int y;
/ 16 | 4 / uint32_t axis;
/ 20 | 4 / int32_t value;
/ 24 | 4 */ uint32_t modifiers;

                       /* total size (bytes):   28 */
                     }

Fix increases the size of messageData appropriately and adds a
static_assert() to make sure the program will not compile rather
than trying to corrupt the memory.

[woutermeek]

@dwrobel is still needed with the current master?

[dwrobel]

@dwrobel is still needed with the current master?

I'm sorry, I can't tell you as I'm not working on that any longer.