Fixing bug with logging &optional records.

Closes #476.

src/LogMgr.cc

@@ -1089,7 +1089,7 @@ LogVal** LogMgr::RecordToFilterVals(Stream* stream, Filter* filter,
 			if ( ! val )
 				{
 				// Value, or any of its parents, is not set.
-				vals[i] = new LogVal(type, false);
+				vals[i] = new LogVal(filter->fields[i]->type, false);
 				break;
 				}
 			}

testing/btest/Baseline/logging.unset-record/testing.log

@@ -0,0 +1,3 @@
+# a.val1	a.val2	b
+-	-	6
+1	2	3

testing/btest/logging/unset-record.log

@@ -0,0 +1,28 @@
+#
+# @TEST-EXEC: bro %INPUT
+# @TEST-EXEC: btest-diff testing.log
+
+redef enum Log::ID += { TESTING };
+
+type Foo: record {
+	val1: count;
+	val2: count;
+} &log;
+
+type Bar: record {
+	a: Foo   &log &optional;
+	b: count &log;
+};
+
+event bro_init()
+{
+    Log::create_stream(TESTING, [$columns=Bar]);
+
+    local x: Bar;
+
+    x = [$b=6];
+    Log::write(TESTING, x);
+
+    x = [$a=[$val1=1,$val2=2], $b=3];
+    Log::write(TESTING, x);
+}