json_view: a value that is not found has no bytes in its exception context

Keeping the byte range of the root value (#5990) dropped the found flag of
value_path(), but a root has no tokens and is found, while a view of a value
that was removed from the document is not found. Without the flag, the
removed value got the bytes of its stale node, and
"json_view exceptions name the path and the bytes of the value" failed on
the macOS jobs with JSON_DIAGNOSTICS and JSON_DIAGNOSTIC_POSITIONS.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

single_include/nlohmann/json_view.hpp

@@ -5080,8 +5080,12 @@ std::string diagnostics(const error_site site)
     std::string context;
 #if JSON_DIAGNOSTICS
     std::vector<std::string> tokens;
-    // a value that is not found leaves no tokens, like the root
-    static_cast<void>(edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens));
+    const bool found = edited ? value_path<true>(d, site.value(), tokens) : value_path<false>(d, site.value(), tokens);
+    if (!found)
+    {
+        // a value that is not found has no path, and with it no bytes
+        return context;
+    }
     if (!tokens.empty())
     {
         // the root value has no path, but still has a byte range