refactor end_of_field helper into more readable version

Author: ben-schwen

src/fread.c

@@ -349,6 +349,10 @@ static inline bool end_of_field(const char *ch)
   // \0 (maybe more than one) before eof are part of field and do not end it; eol() returns false for \0 but the ch==eof will return true for the \0 at eof.
   // Comment characters terminate a field immediately and take precedence over separators.
   return *ch == sep || ((uint8_t)*ch <= 13 && (ch == eof || eol(&ch))) || (commentChar && *ch == commentChar);
+  if (*ch == sep) return true;
+  if ((uint8_t)*ch <= 13 && (ch == eof || eol(&ch))) return true;
+  if (!commentChar) return false;
+  return *ch == commentChar;
 }
 
 static inline const char *end_NA_string(const char *start)