Fix FST trace initial time stamp. (#2264)

If the first dump was not at time zero, then the FST trace used
to contain the initial values as if they were set at time zero. Now
they only appear at the time the first dump call is actually made,
and hence match the VCD trace exactly.

include/verilated_fst_c.cpp

@@ -230,6 +230,7 @@ void VerilatedFst::dump(vluint64_t timeui) {
         return;
     }
     m_minNextDumpTime = timeui + 1;
+    fstWriterEmitTimeChange(m_fst, timeui);
     if (VL_UNLIKELY(m_fullDump)) {
         m_fullDump = false;  // No more need for next dump to be full
         for (vluint32_t ent = 0; ent < m_callbacks.size(); ++ent) {
@@ -238,7 +239,6 @@ void VerilatedFst::dump(vluint64_t timeui) {
         }
         return;
     }
-    fstWriterEmitTimeChange(m_fst, timeui);
     for (vluint32_t ent = 0; ent < m_callbacks.size(); ++ent) {
         VerilatedFstCallInfo* cip = m_callbacks[ent];
         (cip->m_changecb)(this, cip->m_userthis, cip->m_code);

test_regress/t/t_trace_two_dumpfst_cc.out

@@ -1,5 +1,5 @@
 $date
-	Mon Apr  6 08:10:23 2020
+	Sat Apr 18 22:18:21 2020
 
 $end
 $version
@@ -21,10 +21,11 @@ $upscope $end
 $upscope $end
 $enddefinitions $end
 $dumpvars
-1!
-b00000000000000000000000000000001 "
-b00000000000000000000000000000000 #
+#10
 b00000000000000000000000000000001 $
+b00000000000000000000000000000000 #
+b00000000000000000000000000000001 "
+1!
 #15
 0!
 #20
@@ -83,5 +84,5 @@ b00000000000000000000000000001010 "
 0!
 #110
 1!
-b00000000000000000000000000001011 "
 b00000000000000000000000000001100 #
+b00000000000000000000000000001011 "

test_regress/t/t_trace_two_portfst_cc.out

@@ -1,5 +1,5 @@
 $date
-	Mon Apr  6 08:24:52 2020
+	Sat Apr 18 22:19:21 2020
 
 $end
 $version
@@ -21,10 +21,11 @@ $upscope $end
 $upscope $end
 $enddefinitions $end
 $dumpvars
-1!
-b00000000000000000000000000000001 "
-b00000000000000000000000000000000 #
+#10
 b00000000000000000000000000000001 $
+b00000000000000000000000000000000 #
+b00000000000000000000000000000001 "
+1!
 #15
 0!
 #20
@@ -83,5 +84,5 @@ b00000000000000000000000000001010 "
 0!
 #110
 1!
-b00000000000000000000000000001011 "
 b00000000000000000000000000001100 #
+b00000000000000000000000000001011 "