not block if assertion error when counting flops

Summary:
fvcore flops calculator throws on this error:

KeyError: 'Only support flattening dictionaries if keys are str.'

Setting flops to some value so it doesn't enter pdb mode.

Reviewed By: stephenyan1231

Differential Revision: D32144492

fbshipit-source-id: 604cd4660cea9ffbfb3f1da35d32e06ccf607a50

d2go/utils/flop_calculator.py

@@ -87,6 +87,7 @@ def dump_flops_info(model, inputs, output_dir, use_eval_mode=True):
             "Failed to estimate flops using detectron2's FlopCountAnalysis. "
             f"Error written to {output_file}."
         )
+        flops = float("nan")
     return flops