BibTeX parser: fix handling of `%` in url field.

`%` does not function as a comment character inside `url`
(where URL-encoding is common).

Commit 6fb2973a582116cd515c6f7e68794cca22955511 mistakenly
took this reassignment of `%` to be a general feature of
braced (but not quoted) BibTeX fields.

This commit restores the correct behavior of `%` in braced fields
other than `url`, and corrects the behavior of `%` in `url`
when the value is quoted.

Closes #7678 (again).

1 files changed, 31 insertions, 0 deletions

diff --git a/test/command/7678.md b/test/command/7678.md
new file mode 100644
index 000000000..b6a09ef20
--- /dev/null
+++ b/test/command/7678.md
@@ -0,0 +1,31 @@
+```
+% pandoc -f bibtex -t csljson
+@misc{doe,
+  author = "Jane Doe",
+  title = "Work",
+  year = "2021",
+  url = "%20and%20"
+}
+^D
+[
+  {
+    "URL": "%20and%20",
+    "author": [
+      {
+        "family": "Doe",
+        "given": "Jane"
+      }
+    ],
+    "id": "doe",
+    "issued": {
+      "date-parts": [
+        [
+          2021
+        ]
+      ]
+    },
+    "title": "Work",
+    "type": ""
+  }
+]
+```