Describe the bug

Setting Strings in parallel in subarray to zero for one or more subarrays causes simulation crash.

To Reproduce

Steps to reproduce the behavior:

1. Create any Detailed PV case.
2. On System Design page, set Strings in parallel in subarray for Subarray 1 to zero.
3. Click Simulate.
4. SAM crashes.

Expected behavior

SSC modules pvsamv1 should generate a simulation error like it does if modules per string is zero:

fail(subarray1_modules_per_string, positive): 0
Simulation pvsamv1 failed :fail(subarray1_modules_per_string, positive): 0
gen not assigned
Simulation grid failed :gen not assigned