Fix invalid iterator in CloseCdm

[ Merge of http://go/ag/5334065 and http://go/wvgerrit/65122 ]

Sessions were not being correctly released when CloseCdm() was called.
Broadcom noticed this issue and proposed the fix.

Bug: 117876077
Test: WV unit/integration tests, GtsMediaTestCases and playback tests
Change-Id: I8800744f2396f0955c76d5f3e187a69fe04330f6

libwvdrmengine/cdm/src/wv_content_decryption_module.cpp

@@ -434,9 +434,12 @@ CdmResponseType WvContentDecryptionModule::CloseCdm(
       return UNKNOWN_ERROR;
     }
     // Remove any sessions that point to this engine.
-    for (auto session_it : cdm_by_session_id_) {
-      if (session_it.second == it->second.cdm_engine.get()) {
-        cdm_by_session_id_.erase(session_it.first);
+    for (auto session_it = cdm_by_session_id_.begin();
+         session_it != cdm_by_session_id_.end();) {
+      if (session_it->second == it->second.cdm_engine.get()) {
+        session_it = cdm_by_session_id_.erase(session_it);
+      } else {
+        ++session_it;
       }
     }
     cdms_.erase(it);