Check list length before handling the godoc result

[paco0x]

Fix the index out of range issue when handling empty result from gopls

When using go_info_mode='gopls', there's an index-out-of-range issue when handling empty result from gopls. This occurs frequently when you turned on go_auto_type_info and the cursor hovered on something like an imported package name.

For example, use the code above:

fmt.Println("test")

When running :GoInfo on the word fmt, vim says:

vim-go: [info] SUCCESS
Error detected while processing function <SNR>153_on_stdout[1]..<SNR>153_neocb[58]..286[33]..<SNR>152_hoverHandler[9]..<SNR>152_info[1]..<SNR>152_infoFromHoverContent:
line    1:
E684: list index out of range: 0
Press ENTER or type command to continue
Error detected while processing function <SNR>153_on_stdout[1]..<SNR>153_neocb[58]..286[33]..<SNR>152_hoverHandler[9]..<SNR>152_info[1]..<SNR>152_infoFromHoverContent:
line    1:
E15: Invalid expression: a:content[0]
Press ENTER or type command to continue
Error detected while processing function <SNR>153_on_stdout[1]..<SNR>153_neocb:
line   58:
E170: Missing :endwhile
Press ENTER or type command to continue

[bhcleek]

Thank you.