Only do expensive area coverage calculation if there where blocks loaded from database.

If there are not, nothing changed, so nothing to recalculate.
Takes a good deal from the clock.

cmd/mtseeder/main.go

@@ -8,6 +8,8 @@ import (
 	"flag"
 	"fmt"
 	"log"
+	"os"
+	"runtime/pprof"
 
 	"bitbucket.org/s_l_teichmann/mtsatellite/common"
 )
@@ -27,6 +29,7 @@ func main() {
 		transparent      bool
 		transparentDim   float64
 		version          bool
+		cpuProfile       string
 	)
 
 	defaultBgColor := common.ColorToHex(common.BackgroundColor)
@@ -60,6 +63,7 @@ func main() {
 		"td", common.DefaultTransparentDim*100.0,
 		"Extra fimming of transparent nodes each depth meter in percent. (shorthand)")
 	flag.BoolVar(&version, "version", false, "Print version and exit.")
+	flag.StringVar(&cpuProfile, "c", "", "Dump pprof profile to file.")
 
 	flag.Parse()
 
@@ -67,6 +71,15 @@ func main() {
 		common.PrintVersionAndExit()
 	}
 
+	if cpuProfile != "" {
+		f, err := os.Create(cpuProfile)
+		if err != nil {
+			log.Fatal(err)
+		}
+		pprof.StartCPUProfile(f)
+		defer pprof.StopCPUProfile()
+	}
+
 	bg := common.ParseColorDefault(bgColor, common.BackgroundColor)
 
 	if !skipBaseLevel {