[csv-] use newline='' for opening files

The csv library documentation says
"If newline='' is not specified, newlines embedded inside quoted fields
will not be interpreted correctly [...] . It should always be safe
to specify newline='', since the csv module does its own (universal)
newline handling."
https://docs.python.org/3/library/csv.html#id4

visidata/loaders/csv.py

@@ -43,7 +43,7 @@ def iterload(self):
  import csv
  csv.field_size_limit(2**31-1) #288 Windows has max 32-bit
 
- with self.open_text_source() as fp:
+ with self.open_text_source(newline='') as fp:
  if options.safety_first:
  rdr = csv.reader(removeNulls(fp), **options.getall('csv_'))
  else:

visidata/text_source.py

@@ -44,9 +44,9 @@ def __exit__(self, *args, **kwargs):
 
 
 @BaseSheet.api
-def open_text_source(sheet):
+def open_text_source(sheet, newline=None):
  'Open sheet source as text, using sheet options for encoding and regex_skip.'
- fp = sheet.source.open(encoding=sheet.options.encoding, encoding_errors=sheet.options.encoding_errors)
+ fp = sheet.source.open(encoding=sheet.options.encoding, encoding_errors=sheet.options.encoding_errors, newline=newline)
  regex_skip = sheet.options.regex_skip
  if regex_skip:
  return FilterFile(fp, regex_skip, sheet.regex_flags())