HDF5: Fix crash w/ full_frame + no tileshape param

[sk1p]

Contributor Checklist:

• I have added a changelog entry for my contribution
• I have added/updated test cases

[codecov]

Codecov Report

Merging #608 into master will increase coverage by 0.95%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #608      +/-   ##
==========================================
+ Coverage   57.47%   58.43%   +0.95%     
==========================================
  Files         208      209       +1     
  Lines        7923     8101     +178     
  Branches     1038     1096      +58     
==========================================
+ Hits         4554     4734     +180     
- Misses       3175     3177       +2     
+ Partials      194      190       -4     

Impacted Files	Coverage Δ
src/libertem/utils/async_utils.py	100.00% <0.00%> (ø)
src/libertem/io/dataset/hdf5.py	90.62% <0.00%> (+1.25%)	⬆️
src/libertem/api.py	89.69% <0.00%> (+1.63%)	⬆️
src/libertem/web/dataset.py	77.52% <0.00%> (+2.23%)	⬆️
src/libertem/web/base.py	95.18% <0.00%> (+3.31%)	⬆️
src/libertem/web/jobs.py	70.96% <0.00%> (+4.58%)	⬆️
src/libertem/io/dataset/__init__.py	91.30% <0.00%> (+18.57%)	⬆️

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