check getCurrentBlock return value validity

[orenyodfat]

getCurrentBlock might return null in some cases.
while using it there is a need to check for its return value.

especially here
if the return value is null , a special care must be taken .
(This is the current case with Biconomy pr) .

[tibetsprague]

when you say a special care, do you mean we should still show the notification or not? it looks to me like there is a real error preventing access to the subgraph with Biconomy, in that case I think we want to know that and report that to the user

[dkent600]

An inability to use getBlock does not mean we can't access the subgraph.

[tibetsprague]

should we just remove the block check then in the subgraph warning code? or only use it if we get a block number