BUG/MINOR: config: Stopped parsing upon unmatched environment variables

When an environment variable could not be matched by getenv(), the
current character to be parsed by parse_line() from <in> variable
is the trailing double quotes. If nothing is done in such a case,
this character is skipped by parse_line(), then the following spaces
are parsed as an empty argument.

To fix this, skip the double quotes character and the following spaces
to make <in> variable point to the next argument to be parsed.

Thank you to @sigint2 for having reported this issue in GH #2367.

Must be backported as far as 2.4.

src/tools.c

@@ -5809,6 +5809,21 @@ uint32_t parse_line(char *in, char *out, size_t *outlen, char **args, int *nbarg
 					}
 				}
 			}
+			else {
+				/* An unmatched environment variable was parsed.
+				 * Let's skip the trailing double-quote character
+				 * and spaces.
+				 */
+				if (likely(*var_name != '.') && *in == '"') {
+					in++;
+					while (isspace((unsigned char)*in))
+						in++;
+					if (dquote) {
+						dquote = 0;
+						quote = NULL;
+					}
+				}
+			}
 			word_expand = NULL;
 		}
 		else {