config: create a copy of the section name

The parsing context keeps a pointer to the current section name. This
is used when logging errors.

However, the pointer was into a buffer allocated by getline(). This
buffer are often re-used in the next call to getline(), or free:d.

Regardless, the section name pointer is invalid after the next call to
getline(), which meant all error messages were logging a correct
section name.

CHANGELOG.md

@@ -49,6 +49,7 @@
 
 * Regression: `letter-spacing` resulting in a “not a valid option”
   error (https://codeberg.org/dnkl/foot/issues/795).
+* Regression: bad section name in configuration error messages.
 
 
 ### Security

config.c

@@ -2469,9 +2469,11 @@ parse_config_file(FILE *f, struct config *conf, const char *path, bool errors_ar
             continue;                           \
     }
 
+    char *section_name = xstrdup("main");
+
     struct context context = {
         .conf = conf,
-        .section = "main",
+        .section = section_name,
         .path = path,
         .lineno = 0,
         .errors_are_fatal = errors_are_fatal,
@@ -2539,7 +2541,9 @@ parse_config_file(FILE *f, struct config *conf, const char *path, bool errors_ar
                 error_or_continue();
             }
 
-            context.section = &key_value[1];
+            free(section_name);
+            section_name = xstrdup(&key_value[1]);
+            context.section = section_name;
 
             /* Process next line */
             continue;
@@ -2569,10 +2573,12 @@ parse_config_file(FILE *f, struct config *conf, const char *path, bool errors_ar
             error_or_continue();
     }
 
+    free(section_name);
     free(_line);
     return true;
 
 err:
+    free(section_name);
     free(_line);
     return false;
 }