Assert non-NULL serial

If no serial is passed, then the command would work if there is exactly
one device connected, but will fail with multiple devices.

To avoid such cases, ensure that a serial is always provided.

app/src/adb/adb.c

@@ -221,6 +221,8 @@ sc_adb_forward(struct sc_intr *intr, const char *serial, uint16_t local_port,
     char remote[108 + 14 + 1]; // localabstract:NAME
     sprintf(local, "tcp:%" PRIu16, local_port);
     snprintf(remote, sizeof(remote), "localabstract:%s", device_socket_name);
+
+    assert(serial);
     const char *const adb_cmd[] = {"forward", local, remote};
 
     sc_pid pid = sc_adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd), flags);
@@ -232,6 +234,8 @@ sc_adb_forward_remove(struct sc_intr *intr, const char *serial,
                       uint16_t local_port, unsigned flags) {
     char local[4 + 5 + 1]; // tcp:PORT
     sprintf(local, "tcp:%" PRIu16, local_port);
+
+    assert(serial);
     const char *const adb_cmd[] = {"forward", "--remove", local};
 
     sc_pid pid = sc_adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd), flags);
@@ -246,6 +250,8 @@ sc_adb_reverse(struct sc_intr *intr, const char *serial,
     char remote[108 + 14 + 1]; // localabstract:NAME
     sprintf(local, "tcp:%" PRIu16, local_port);
     snprintf(remote, sizeof(remote), "localabstract:%s", device_socket_name);
+
+    assert(serial);
     const char *const adb_cmd[] = {"reverse", remote, local};
 
     sc_pid pid = sc_adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd), flags);
@@ -257,6 +263,8 @@ sc_adb_reverse_remove(struct sc_intr *intr, const char *serial,
                       const char *device_socket_name, unsigned flags) {
     char remote[108 + 14 + 1]; // localabstract:NAME
     snprintf(remote, sizeof(remote), "localabstract:%s", device_socket_name);
+
+    assert(serial);
     const char *const adb_cmd[] = {"reverse", "--remove", remote};
 
     sc_pid pid = sc_adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd), flags);
@@ -280,7 +288,9 @@ sc_adb_push(struct sc_intr *intr, const char *serial, const char *local,
     }
 #endif
 
+    assert(serial);
     const char *const adb_cmd[] = {"push", local, remote};
+
     sc_pid pid = sc_adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd), flags);
 
 #ifdef __WINDOWS__
@@ -303,7 +313,9 @@ sc_adb_install(struct sc_intr *intr, const char *serial, const char *local,
     }
 #endif
 
+    assert(serial);
     const char *const adb_cmd[] = {"install", "-r", local};
+
     sc_pid pid = sc_adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd), flags);
 
 #ifdef __WINDOWS__
@@ -318,6 +330,8 @@ sc_adb_tcpip(struct sc_intr *intr, const char *serial, uint16_t port,
              unsigned flags) {
     char port_string[5 + 1];
     sprintf(port_string, "%" PRIu16, port);
+
+    assert(serial);
     const char *const adb_cmd[] = {"tcpip", port_string};
 
     sc_pid pid = sc_adb_execute(serial, adb_cmd, ARRAY_LEN(adb_cmd), flags);
@@ -374,6 +388,7 @@ sc_adb_disconnect(struct sc_intr *intr, const char *ip_port, unsigned flags) {
 char *
 sc_adb_getprop(struct sc_intr *intr, const char *serial, const char *prop,
                unsigned flags) {
+    assert(serial);
     const char *const adb_cmd[] = {"shell", "getprop", prop};
 
     sc_pipe pout;
@@ -434,6 +449,7 @@ sc_adb_get_serialno(struct sc_intr *intr, unsigned flags) {
 
 char *
 sc_adb_get_device_ip(struct sc_intr *intr, const char *serial, unsigned flags) {
+    assert(serial);
     const char *const cmd[] = {"shell", "ip", "route"};
 
     sc_pipe pout;