VecLoad_HDF5: uninitialized block size is indicated by bs==-1, not bs==1

Conflicts:
	src/vec/vec/utils/vecio.c
Fixed HDF5 VecLoad

(cherry picked from commit 9c95f1f0bf874a9750b779c67517fdf53a7067b2)
Merge branch 'maint-3.2' into maint

* maint-3.2:
  Fixed HDF5 VecLoad (already present in 'maint')