Fix text input event segfault

The text input control_event was initially designed for mapping
SDL_TextInputEvent, limited to 32 characters.

For simplicity, the copy/paste feature was implemented using the same
control_event: it just sends the text to paste.

However, the pasted text might have a length breaking some assumptions:
 - on the client, the event max-size was smaller than the text
   max-length,
 - on the server, the raw buffer storing the events was smaller than the
   max event size.

Fix these inconsistencies, and encode the length on 2 bytes, to accept
more than 256 characters.

Fixes <https://github.com/Genymobile/scrcpy/issues/10>.

app/tests/test_control_event_serialize.c

@@ -35,16 +35,36 @@ static void test_serialize_text_event() {
 
     unsigned char buf[SERIALIZED_EVENT_MAX_SIZE];
     int size = control_event_serialize(&event, buf);
-    assert(size == 15);
+    assert(size == 16);
 
     const unsigned char expected[] = {
         0x01, // CONTROL_EVENT_TYPE_KEYCODE
-        0x0d, // text length
+        0x00, 0x0d, // text length
         'h', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd', '!', // text
     };
     assert(!memcmp(buf, expected, sizeof(expected)));
 }
 
+static void test_serialize_long_text_event() {
+    struct control_event event;
+    event.type = CONTROL_EVENT_TYPE_TEXT;
+    char text[TEXT_MAX_LENGTH];
+    memset(text, 'a', sizeof(text));
+    event.text_event.text = text;
+
+    unsigned char buf[SERIALIZED_EVENT_MAX_SIZE];
+    int size = control_event_serialize(&event, buf);
+    assert(size == 3 + sizeof(text));
+
+    unsigned char expected[3 + TEXT_MAX_LENGTH];
+    expected[0] = 0x01; // CONTROL_EVENT_TYPE_KEYCODE
+    expected[1] = 0x01;
+    expected[2] = 0x2c; // text length (16 bits)
+    memset(&expected[3], 'a', TEXT_MAX_LENGTH);
+
+    assert(!memcmp(buf, expected, sizeof(expected)));
+}
+
 static void test_serialize_mouse_event() {
     struct control_event event = {
         .type = CONTROL_EVENT_TYPE_MOUSE,
@@ -114,6 +134,7 @@ static void test_serialize_scroll_event() {
 int main() {
     test_serialize_keycode_event();
     test_serialize_text_event();
+    test_serialize_long_text_event();
     test_serialize_mouse_event();
     test_serialize_scroll_event();
     return 0;