[osh2oil] Tweaks to avoid crashes.

- Avoid a crash in the special case of the empty file.
  - The line_id is -1 only in that case, which makes logical sense, but
    caused a crash.
  - We might want to have no zero-length spans then?  Or say that
    Eof_Real doesn't produce a span?

- Don't crash on ExtGlobPart.  Though I'm not sure exactly how to
  translate this.

Also: categorize a few more wild errors.

test/wild-not-osh.txt

@@ -11,3 +11,9 @@ esoteric/setup.shl/bin/setup  # associative array ambiguity (key should be quote
exp/shootout/timing.sh  # the $(( )) ambiguity 

linux-4.8.7/tools/perf/perf-with-kcore.sh  # another $(( )) ambiguity

# These four have unexpected arguments to exit.  We statically parse that.
shell/modernish/uninstall.sh
shell/modernish/share/doc/modernish/examples/get-firefox.sh
shell/modernish/share/doc/modernish/examples/copy-timestamps.sh
shell/modernish/share/doc/modernish/examples/testshells.sh

test/wild-not-shell.txt

@@ -18,3 +18,6 @@ freebsd-11.1/usr.bin/tr/tests/regress.sh
freebsd-11.1/usr.bin/sed/tests/regress.sh
freebsd-11.1/usr.bin/join/tests/regress.sh
linux-4.8.7/tools/perf/perf-completion.sh

# This is awk, not shell!
linux-4.8.7/scripts/ld-version.sh

tools/osh2oil.py

@@ -70,6 +70,11 @@ def PrintArena(arena):

def PrintSpans(arena):
  """Just to see spans."""
  if len(arena.spans) == 1:  # Special case for line_id == -1
    print('Empty file with EOF span on invalid line:')
    print('%s' % arena.spans[0])
    return

  for i, span in enumerate(arena.spans):
    line = arena.GetLine(span.line_id)
    piece = line[span.col : span.col + span.length]
@@ -78,6 +83,10 @@ def PrintSpans(arena):


def PrintAsOil(arena, node, debug_spans):
  if len(arena.spans) == 1:  # Special case for line_id == -1
    # Nothing to print; would crash otherwise.
    return

  #print node
  #print(spans)
  if debug_spans:
@@ -1277,6 +1286,14 @@ def DoWordPart(self, node, local_symbols, quoted=False):
    elif node.tag == word_part_e.EmptyPart:
      pass

    elif node.tag == word_part_e.ExtGlobPart:
      # Change this into a function?  It depends whether it is used as
      # a glob or fnmatch.
      # 
      # Example of glob:
      # cloud/sandstorm/make-bundle.sh
      pass

    else:
      raise AssertionError(node.__class__.__name__)