MT#65603 AmSipMsg: fix sip option parser

Do not use the original iterator's position,
when removing the first token from something like:
`Supported: timer, path, replaces`

Instead build the remaining option list by appending
only those kept, trimmed tokens with commas between them.

(P.S.: this is not related to the latest SST changes)

Change-Id: I5a274072dbbc336494a0802ff7e80f0bf0b51813

core/AmSipMsg.cpp

@@ -195,13 +195,16 @@ void removeOptionTag(string& hdrs, const string& hdr_name, const string& tag) {
   bool found = false;
   for (std::vector<string>::iterator it=options_v.begin();
        it != options_v.end(); it++) {
-    if (trim(*it, " ")==tag) {
+    string option = trim(*it, " ");
+    if (option == tag) {
       found = true;
       continue;
     }
-    if (it != options_v.begin())
-      o_hdr = ", ";
-    o_hdr+=*it;
+    if (option.empty())
+      continue;
+    if (!o_hdr.empty())
+      o_hdr += ", ";
+    o_hdr += option;
   }
   if (!found)
     return;