added catch statement for leaflet_sorter_3

TCL/polarDensity_for_DTA.tcl

@@ -282,13 +282,23 @@ proc leaflet_sorter_2 {atsel_in refsel_in frame_i} {
 ;# Compares lipid's COM z component to local midplane and sorts accordingly.
 proc leaflet_sorter_3 {atsel_in frame_i} {
     set lipidsel [atomselect top $atsel_in frame $frame_i]
+    puts [$lipidsel num]
     set lipid_com [measure center $lipidsel weight mass]
     set lipid_x [lindex $lipid_com 0]
     set lipid_y [lindex $lipid_com 1]
     set lipid_z [lindex $lipid_com 2]
 
     set local_surfaces [atomselect top "name PO4 GL1 GL2 AM1 AM2 and (x-$lipid_x)*(x-$lipid_x)+(y-$lipid_y)*(y-$lipid_y)<200" frame $frame_i]
-    set local_midplane [lindex [measure center $local_surfaces weight mass] 2]
+
+    if { [catch {set local_midplane [lindex [measure center $local_surfaces weight mass] 2]} errid] } {
+        puts stderr "$errid"
+        $lipidsel set user2 3
+        $lipidsel delete
+        $local_surfaces delete
+        return 3
+    } else {
+        set local_midplane [lindex [measure center $local_surfaces weight mass] 2]
+    }
     $local_surfaces delete
 
     if {$lipid_z < $local_midplane} {