Fix fread crashes

[tlapak]

Closes #5041
closes #4774

Unbalanced quotes out of sample in a character column would be registered as a type bump but character is already the highest type. The segfault occurred in the next attempt to select the corresponding reader on what is currently line 2272 of fread.c

While testing my fix I stumbled upon another segfault that I also fixed here by stealing the fix for #4644, which happened for essentially the same reasons. The following would segfault before:

fread(paste0(paste(rep(c('1; 2'), 100), collapse = '\n'), c('\n"a";2\n1; 2\n'), paste(rep(c('1; 2'), 100), collapse = '\n')),
fill = TRUE, verbose = TRUE, header = FALSE)

Toggling any of the options prevents the segfault. Again the type bump must occur out of sample. I was slightly stumped by varying sampling behaviour of fread.