fix: SrtCaller and SrtSession crash (#4328)

1.修改SrtCaller 多线程发送造成的crash
2.修改SrtCaller 接收的期望外的控制包可能造成的空指针引用
3.修改异常的streamid ext可能造成的crash

srt/HSExt.cpp

@@ -83,8 +83,10 @@ bool HSExtStreamID::loadFromData(uint8_t *buf, size_t len) {
         ptr += 4;
     }
     char zero = 0x00;
-    if (streamid.back() == zero) {
-        streamid.erase(streamid.find_first_of(zero), streamid.size());
+    if (!streamid.empty()) {
+        if (streamid.back() == zero) {
+            streamid.erase(streamid.find_first_of(zero), streamid.size());
+        }
     }
     return true;
 }