Position coincident page marks in the correct order (#1274)

* Position coincident page marks in the correct order

If Pg123 and Pg124 were at the same location in the file,
usually because Pg123 is blank, then when the page locations
are loaded from the bin file and positioned in the text widget
using "marks", the mark for Pg124 was inserted at the location
where Pg123's mark was, and ended up before it in the text
widget's internal list of marks.

Loading the marks in reverse order means that coincident
marks appear in alphanumeric order,  which is preferable.

This was assumed to be the case by the HTML generation
code when set to skip coincident pagenum spans. So this
fixes #1272

* Revert "Position coincident page marks in the correct order"

This reverts commit f366b5e.

* Sort pagemarks correctly when adding HTML pagenums

Although `markNext` iterates through the marks in order of their
location, it does not guarantee an order when two marks have the
same location. This could lead to some page numbers that directly
followed blank pages not being output to the HTML file.

To resolve it, just sort a list of page markers and use that, rather
than iterating through the markers in the file.

Fixes #1272

src/lib/Guiguts/HTMLConvert.pm

@@ -1250,20 +1250,19 @@ sub html_convert_sidenotes {
 sub html_convert_pageanchors {
     my $textwindow = $::textwindow;
     ::working("Inserting Page Number Markup");
-    $|++;
     my @pagerefs;    # keep track of first/last page markers at the same position
-    my $tempcounter;
-    my $mark = '1.0';
-    while ( $textwindow->markPrevious($mark) ) {
-        $mark = $textwindow->markPrevious($mark);
-    }
 
     my $closure = voidclosure();
 
-    # Work through all the text markers
-    while ( $mark = $textwindow->markNext($mark) ) {
-        next unless $mark =~ m{Pg(\S+)};              # Only look at page markers
-        my $markindex = $textwindow->index($mark);    # Get page marker's index
+    # Get a correctly sorted list of page markers - if two markers are at the
+    # same location, the order returned by markNext is not defined, but we need
+    # them ordered by png.
+    my @pagemarklist = sort grep ( /^Pg\S+$/, $textwindow->markNames );
+
+    for my $idx ( 0 .. $#pagemarklist ) {
+        my $mark      = $pagemarklist[$idx];
+        my $markindex = $textwindow->index($mark);                                # Get page marker's index
+        my $marknext  = $idx < $#pagemarklist ? $pagemarklist[ $idx + 1 ] : "";
 
         # This is the custom page label
         my $num = $::pagenumbers{$mark}{label};
@@ -1283,12 +1282,6 @@ sub html_convert_pageanchors {
             push @pagerefs, $num;
         }
 
-        # Find next page marker & its index
-        my $marknext = $mark;
-        while ( $marknext = $textwindow->markNext($marknext) ) {
-            last if $marknext =~ m{Pg(\S+)};
-        }
-
         # If no more marks (reached end of file) or there are word characters between the
         # current mark and the next, then convert batch of accumulated page markers to a string
         my $pagereference = '';