Fix assertion error when stats requested and 0 threads scheduled

CHANGELOG

@@ -1,5 +1,12 @@
 # Nmap Changelog ($Id$); -*-text-*-
 
+o [NSE] Fix a crash that happened when trying to print the percent done of 0
+  NSE script threads:
+    timing.cc:710 bool ScanProgressMeter::printStats(double, const timeval*): Assertion 'ltime' failed.
+  This would happen if no scripts were scheduled in a scan phase and the user
+  pressed a key or specified a short --stats-every interval. Reported by
+  Richard Petrie. [Daniel Miller]
+
 o [NSE] ssl-enum-ciphers will give a failing score to any server with an RSA
   certificate whose public key uses an exponent of 1. [Daniel Miller]
 

nse_main.lua

@@ -958,7 +958,8 @@ local function run (threads_iter, hosts)
     end
 
     local nr, nw = table_size(running), table_size(waiting);
-    if cnse.key_was_pressed() then
+    -- total may be 0 if no scripts are running in this phase
+    if total > 0 and cnse.key_was_pressed() then
       print_verbose(1, "Active NSE Script Threads: %d (%d waiting)",
           nr+nw, nw);
       progress("printStats", 1-(nr+nw)/total);
@@ -972,7 +973,7 @@ local function run (threads_iter, hosts)
               (gsub(traceback(co), "\n", "\n\t")));
         end
       end
-    elseif progress "mayBePrinted" then
+    elseif total > 0 and progress "mayBePrinted" then
       if verbosity() > 1 or debugging() > 0 then
         progress("printStats", 1-(nr+nw)/total);
       else