logd: last iterator initialized incorrectly

last should start with mLogElements.end() and be updated as
we iterate to find a matching time entry in the list. Since
it is impossible(sic) for a newer start time to be supplied
than the list, the incorrect iterator initialization should
be inconsequential, but if it ever happens this change will
behave correctly and dump nothing.

Test: gTest liblog-unit-tests, logd-unit-tests and logcat-unit-tests
Bug: 36536248
Bug: 36608728
Change-Id: I96998c4b713258f29d5db2e24a83ae562ddf3420
diff --git a/logd/LogBuffer.cpp b/logd/LogBuffer.cpp
index 12deb7b..86ea6b4 100644
--- a/logd/LogBuffer.cpp
+++ b/logd/LogBuffer.cpp
@@ -1088,12 +1088,12 @@
         // client wants to start from the beginning
         it = mLogElements.begin();
     } else {
-        LogBufferElementCollection::iterator last = mLogElements.begin();
+        LogBufferElementCollection::iterator last;
         // 30 second limit to continue search for out-of-order entries.
         log_time min = start - log_time(30, 0);
         // Client wants to start from some specified time. Chances are
         // we are better off starting from the end of the time sorted list.
-        for (it = mLogElements.end(); it != mLogElements.begin();
+        for (last = it = mLogElements.end(); it != mLogElements.begin();
              /* do nothing */) {
             --it;
             LogBufferElement* element = *it;