LogMessage::UpdateMinLogSeverity: Don't ignore all but the last stream

Bug reported by andrey.semashev@gmail.com.

Bug: webrtc:9364
Change-Id: I49ef8969afc5bcd55d9e5ecbe644fe190a436c7b
Reviewed-on: https://webrtc-review.googlesource.com/83124
Reviewed-by: Jonas Olsson <jonasolsson@webrtc.org>
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23578}
diff --git a/rtc_base/logging.cc b/rtc_base/logging.cc
index 8b3d9f1..5e035a6 100644
--- a/rtc_base/logging.cc
+++ b/rtc_base/logging.cc
@@ -357,8 +357,9 @@
 void LogMessage::UpdateMinLogSeverity()
     RTC_EXCLUSIVE_LOCKS_REQUIRED(g_log_crit) {
   LoggingSeverity min_sev = g_dbg_sev;
-  for (auto& kv : streams_) {
-    min_sev = std::min(g_dbg_sev, kv.second);
+  for (const auto& kv : streams_) {
+    const LoggingSeverity sev = kv.second;
+    min_sev = std::min(min_sev, sev);
   }
   g_min_sev = min_sev;
 }