[trunk] Perspective/Envelope LPE fails to recognise capitalised attribute names

[Parcly Taxel]

Opening or previewing (in the open or save dialogues) the attached file in inkscape-trunk r14055 on Trisquel 7.0 (based on Trusty) leads to a crash. However, if lines 32 and 33 are changed in a text editor so that their last four attributes are in lowercase (i.e. up_left_point, up_right_point, down_left_point, down_right_point), the problem disappears.

I am convinced that the bug arose from r14052, which failed to ensure compatibility with older files using the Perspective/Envelope LPE with the capitalised attribute names.

[su_v (suv-lp)]

On OS X 10.7.5: crash on load
- not reproduced with 0.91+devel rev 14048
- reproduced with 0.91+devel rev 14055

[su_v (suv-lp)]

Crash seems related to changing the case in names of attributes stored in the patheffect definition in the <defs> section. Since this specific patheffect was never in a stable release version, it seems ok to me to commit breaking changes to such a "work-in-progress" path effect to recent trunk which are not fully backwards-compatible to earlier trunk builds. Path effects are not (or can't) be finalized with their initial first commit (changes are allowed as long as they have not been part of a stable release).

[su_v (suv-lp)]

@Jabiertxof - could the crash be avoided without reverting the refactoring of the Perspective/Envelope patheffect - e.g. by disabling the effect if stored with old or incompatible attribute names (as happens with other unsupported path effects ("Unknown LPE type specified, LPE stack effectively disabled"))?

[Jabiertxof (jabiertxof)]

Thanks parclytaxel for fill the bug!

[Jabiertxof (jabiertxof)]

The fix reset your current LPE :( but you can reaply it with no crash.