[tools] testbot/web: The Submit page should always provide a property list.

[Francois Gouget]

FormPage expects to be provided with a property list when it calls
GetPropertyDescriptors() at the very latest. So while that method may
return an empty list, returning undef is not allowed.

Signed-off-by: Francois Gouget 
---
The patch reordering the FormPage methods contained a change it 
shouldn't have which broke the submit job page.

The FormPage methods were inconsistent about whether they would 
correctly deal with $self->GetPropertyDescriptors() returning undef 
(this specific issue is in the most used method, GenerateFields()). Now 
they don't accept it and so the subclasses should make sure to always 
provide a property list.

This updates the Submit page accordingly.
---
 testbot/web/Submit.pl | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/testbot/web/Submit.pl b/testbot/web/Submit.pl
index 79d1c8772..472622dd5 100644
--- a/testbot/web/Submit.pl
+++ b/testbot/web/Submit.pl
@@ -665,16 +665,23 @@ sub GetPropertyDescriptors($)
   my ($self) = @_;

# Note that this may be called for different pages. For instance first to
-  # validate the properties of the page 1, then again to generate the form
-  # fields of page 2. See _SetPage().
-  if ($self->{Page} == 1)
+  # validate the page 1 properties, then again to generate the page 2 form
+  # fields. See _SetPage().
+  if ($self->{PropertyDescriptors})
   {
-    $self->{PropertyDescriptors} ||= [
+    # The property descriptors list is already set for $self->{Page}
+  }
+  elsif ($self->{Page} == 1)
+  {
+    $self->{PropertyDescriptors} = [
       CreateBasicPropertyDescriptor("Remarks", "Remarks", !1, !1, "A", 128),
     ];
   }
-  elsif (($self->{Page} == 3 or $self->{Page} == 4) and
-         !$self->{PropertyDescriptors})
+  elsif ($self->{Page} == 2)
+  {
+    $self->{PropertyDescriptors} = []; # no fields, only a collection block
+  }
+  elsif ($self->{Page} == 3 or $self->{Page} == 4)
   {
     if ($self->{Page} == 4)
     {
@@ -960,9 +967,12 @@ sub _SetPage($$)
 {
   my ($self, $Page) = @_;

-  $self->{Page} = $Page;
-  # Changing the page also changes the fields of the HTML form
-  delete $self->{PropertyDescriptors};
+  if ($self->{Page} != $Page)
+  {
+    $self->{Page} = $Page;
+    # Changing the page also changes the fields of the HTML form
+    $self->{PropertyDescriptors} = undef;
+  }
 }

sub OnUnset($)