Verified by creating sample job and removing memory from resources

```
Task "redis" is "running"
Task Resources
CPU        Memory          Disk     IOPS  Addresses
3/100 MHz  976 KiB/10 MiB  300 MiB  0     db: **.**.**.**:20824
```

The current code would merge the job with the output of MinResources causing the nil to be replaced with MemoryMB=helper.IntToPtr(10).  When later `Canonicalize`d, the 10 would cause the default of 300 not to be applied. Running `Canonicalize` on the task itself guarantees that CPU, MemoryMB, and IOPS is set, so we can remove the Merge withMinResources.

…a at all

In testing realized that Resources night not be present at all.  Testing this case caused panic. Added in a means to collect clean defaults in that case.