Last fall, Plug Power (PLUG 0.26%) issued a dire warning. The hydrogen company projected at that time that it didn't have enough liquidity to fund its operations through the next year. That caused investors to worry that it might not be able to continue as a going concern. However, those concerns are now in the rearview mirror. Plug Power has plugged the holes in its liquidity and how has the fuel to continue operating. Here's a look at whether that makes the hydrogen stock a buy. Shoring up its liquidity P ...