Check that b:neomake_signs_cleared exists before reading it.
Check that b:neomake_signs_cleared exists before reading it.

It is set in the buffer where :Neomake is called, but if a maker returns
errors in another buffer, then this variable won't be defined.

nerdrew/neomake,datanoise/neomake,KariusDx/neomake,bonds/neomake,neomake/neomake,euclio/neomake,nerdrew/neomake,codeinabox/neomake,bonds/neomake,neomake/neomake,euclio/neomake