Fix warnings on Windows

fix warnings reported with -Dwarning_level=2 on Windows.

app/src/command.h

@@ -18,6 +18,7 @@
 #   define PRIsizet PRIu32
 # endif
 # define PROCESS_NONE NULL
+# define NO_EXIT_CODE -1u // max value as unsigned
   typedef HANDLE process_t;
   typedef DWORD exit_code_t;
 
@@ -28,6 +29,7 @@
 # define PRIsizet "zu"
 # define PRIexitcode "d"
 # define PROCESS_NONE -1
+# define NO_EXIT_CODE -1
   typedef pid_t process_t;
   typedef int exit_code_t;
 
@@ -35,8 +37,6 @@
 
 #include "config.h"
 
-# define NO_EXIT_CODE -1
-
 enum process_result {
     PROCESS_SUCCESS,
     PROCESS_ERROR_GENERIC,

app/src/main.c

@@ -243,7 +243,7 @@ parse_bit_rate(char *optarg, uint32_t *bit_rate) {
             return false;
         }
     }
-    if (value < 0 || ((uint32_t) -1) / mul < value) {
+    if (value < 0 || ((uint32_t) -1) / mul < (unsigned long) value) {
         LOGE("Bitrate must be positive and less than 2^32: %s", optarg);
         return false;
     }

app/src/scrcpy.c

@@ -103,6 +103,7 @@ sdl_init_and_configure(bool display) {
 // <https://stackoverflow.com/a/40693139/1987178>
 static int
 event_watcher(void *data, SDL_Event *event) {
+    (void) data;
     if (event->type == SDL_WINDOWEVENT
             && event->window.event == SDL_WINDOWEVENT_RESIZED) {
         // called from another thread, not very safe, but it's a workaround!

app/src/stream.c

@@ -44,6 +44,7 @@ stream_recv_packet(struct stream *stream, AVPacket *packet) {
 
     uint64_t pts = buffer_read64be(header);
     uint32_t len = buffer_read32be(&header[8]);
+    SDL_assert(pts == NO_PTS || (pts & 0x8000000000000000) == 0);
     SDL_assert(len);
 
     if (av_new_packet(packet, len)) {
@@ -52,12 +53,12 @@ stream_recv_packet(struct stream *stream, AVPacket *packet) {
     }
 
     r = net_recv_all(stream->socket, packet->data, len);
-    if (r < len) {
+    if (r < 0 || ((uint32_t) r) < len) {
         av_packet_unref(packet);
         return false;
     }
 
-    packet->pts = pts != NO_PTS ? pts : AV_NOPTS_VALUE;
+    packet->pts = pts != NO_PTS ? (int64_t) pts : AV_NOPTS_VALUE;
 
     return true;
 }

app/src/sys/win/command.c

@@ -20,6 +20,7 @@ build_cmd(char *cmd, size_t len, const char *const argv[]) {
 
 enum process_result
 cmd_execute(const char *path, const char *const argv[], HANDLE *handle) {
+    (void) path;
     STARTUPINFOW si;
     PROCESS_INFORMATION pi;
     memset(&si, 0, sizeof(si));