Made template for showing image_field in admin-ui more robust

[vidarl]

Description:

I was not able to reproduce the problem on a fresh 4.6, but on a installation just upgraded to 4.6 (was at some point using 2.5 or maybe even older releases) the database had a lot of images with the following "empty" data in ezcontentobject_attribute.data_text:

<?xml version="1.0" encoding="UTF-8"?>
<ezimage serial_number=""
         is_valid=""
         filename=""
         suffix=""
         basename=""
         dirpath=""
         url=""
         original_filename=""
         mime_type=""
         width=""
         height=""
         alternative_text=""
         alias_key="1293033771"
         timestamp="1086942459" />

In 4.6, the value will simply be null if no image is uploaded. However, in earlier versions it was obviously stored like shown above. And one problem here is that height has a value set to empty string. The admin-ui template requires height to be numeric or a Unsupported operand types: string / string exception will be thrown.

It would be nice if twig had a is numeric test but that is not going to happend. For this use-case it is sufficient to check if value is empty string too

For QA:

Documentation:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[vidarl]

@ViniTou or anyone... Is QA really needed for this PR ?

[ViniTou]

@vidarl
We decided to skip it, I will merge it up.