Bug 29702: Fetch group libraries in a single call

The current code gets all group members, then loops through and fetches the library if there is a
branchcode, or recursively calls itself if a group. This slows down performance.

We can utilize the 'libraries' method to get all child libraries at once, then make a check
for child groups separately

To recreate:
 1 - Add 100 items to a biblio
 2 - Define a library group as a hold group
 3 - Add all libraries to the group
 4 - Set 'Default checkout, hold and return policy'->'Hold pickup library match' = 'Any library'
 5 - place a hold on the record and note load time after patron is selected
 6 - Set 'Default checkout, hold and return policy'->'Hold pickup library match' = 'Patrons hold group'
 7 - place a hold, note longer load time after patron selection
 8 - Apply patch
 9 - note improvement
10 - prove -v t/db_dependent/Koha/Libraries.t

Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>

Koha/Library/Group.pm

@@ -144,14 +144,10 @@ sub all_libraries {
 
     my @libraries;
 
-    my @children = $self->children;
+    push (@libraries, $self->libraries);
+    my @children = $self->children->search({ branchcode => undef });
     foreach my $c (@children) {
-        if ( $c->branchcode ) {
-            push( @libraries, $c->library );
-        }
-        else {
-            push( @libraries, $c->all_libraries );
-        }
+        push( @libraries, $c->all_libraries );
     }
 
     my %seen;