warn if files missing

[brandon1024]

If a file was moved or removed, we should warn the user to re-generate their tag file and skip it.

Error detected while processing function java_support#import#JavaImportKeyword[17]..<SNR>134_FetchResults[1]..java_support#tags#Lookup[11]..<SNR>135_FindPackageForFile:                                                                       
line    5:                                                                                                                                                                                                                                     
E484: Can't open file src/main/java/ca/example/SvcPt.java

[brandon1024]

Since there's a chance there are multiple occurrences of a keyword in a tag file with the same tag name / file name, this can result in a lot of duplicate warning messages.

Instead of warning the user, we'll just ignore that tag if the file doesn't exist.

[brandon1024]

Fixed!