Pigeon::receive: reserve 4kb+64b for std::string (#19951)

* receive: reserve 4kb+64b for std::string

* fix bug

selfdrive/boardd/pigeon.cc

@@ -105,11 +105,11 @@ void PandaPigeon::send(const std::string &s) {
 
 std::string PandaPigeon::receive() {
   std::string r;
-
-  while (true){
-    unsigned char dat[0x40];
+  r.reserve(0x1000 + 0x40);
+  unsigned char dat[0x40];
+  while (r.length() < 0x1000){
     int len = panda->usb_read(0xe0, 1, 0, dat, sizeof(dat));
-    if (len <= 0 || r.length() > 0x1000) break;
+    if (len <= 0) break;
     r.append((char*)dat, len);
   }
 
@@ -190,13 +190,13 @@ void TTYPigeon::send(const std::string &s) {
 
 std::string TTYPigeon::receive() {
   std::string r;
-
-  while (true){
-    char dat[0x40];
+  r.reserve(0x1000 + 0x40);
+  char dat[0x40];
+  while (r.length() < 0x1000){
     int len = read(pigeon_tty_fd, dat, sizeof(dat));
     if(len < 0) {
       handle_tty_issue(len, __func__);
-    } else if (len == 0 || r.length() > 0x1000){
+    } else if (len == 0){
       break;
     } else {
       r.append(dat, len);