[ruby/prism] Fix parser translator tokens for comment-only file

In https://github.com/ruby/prism/pull/3393 I made a mistake.
When there is no previous token, it wraps around to -1. Oops

Additionally, if a comment has no newline then the offset should be kept as is

3c266f1de4

lib/prism/translation/parser/lexer.rb

@@ -281,14 +281,14 @@ module Prism
                 location = range(token.location.start_offset, lexed[index][0].location.end_offset)
                 index += 1
               else
-                value.chomp!
-                location = range(token.location.start_offset, token.location.end_offset - 1)
+                is_at_eol = value.chomp!.nil?
+                location = range(token.location.start_offset, token.location.end_offset + (is_at_eol ? 0 : -1))
 
-                prev_token = lexed[index - 2][0]
+                prev_token = lexed[index - 2][0] if index - 2 >= 0
                 next_token = lexed[index][0]
 
-                is_inline_comment = prev_token.location.start_line == token.location.start_line
-                if is_inline_comment && !COMMENT_CONTINUATION_TYPES.include?(next_token&.type)
+                is_inline_comment = prev_token&.location&.start_line == token.location.start_line
+                if is_inline_comment && !is_at_eol && !COMMENT_CONTINUATION_TYPES.include?(next_token&.type)
                   tokens << [:tCOMMENT, [value, location]]
 
                   nl_location = range(token.location.end_offset - 1, token.location.end_offset)

test/prism/fixtures/comment_single.txt

@@ -0,0 +1 @@
+foo # Bar

test/prism/snapshots/comment_single.txt

@@ -0,0 +1,17 @@
+@ ProgramNode (location: (1,0)-(1,3))
+├── flags: ∅
+├── locals: []
+└── statements:
+    @ StatementsNode (location: (1,0)-(1,3))
+    ├── flags: ∅
+    └── body: (length: 1)
+        └── @ CallNode (location: (1,0)-(1,3))
+            ├── flags: newline, variable_call, ignore_visibility
+            ├── receiver: ∅
+            ├── call_operator_loc: ∅
+            ├── name: :foo
+            ├── message_loc: (1,0)-(1,3) = "foo"
+            ├── opening_loc: ∅
+            ├── arguments: ∅
+            ├── closing_loc: ∅
+            └── block: ∅