editorconfig-core-handle.el: Fix silent misparse

See https://github.com/editorconfig/editorconfig-emacs/issues/380

* lisp/editorconfig-core-handle.el (editorconfig-core-handle--parse-file):
Fix regexp to not inadvertently match LF.  Remove an O(N²) complexity.
Use `line-number-at-pos`.

* lisp/editorconfig.el (editorconfig--get-coding-system): Don't let
errors propagate.

lisp/editorconfig-core-handle.el

@@ -166,10 +166,7 @@ If CONF is not found return nil."
             ;; nil when pattern not appeared yet, "" when pattern is empty ("[]")
             (pattern nil)
             ;; Alist of properties for current PATTERN
-            (props ())
-
-            ;; Current line num
-            (current-line-number 1))
+            (props ()))
         (while (not (eobp))
           (skip-chars-forward " \t\f")
           (cond
@@ -187,7 +184,7 @@ If CONF is not found return nil."
               (setq props nil)
               (setq pattern newpattern)))
 
-           ((looking-at "\\([^=: \t][^=:]*\\)[ \t]*[=:][ \t]*\\(.*?\\)[ \t]*$")
+           ((looking-at "\\([^=: \n\t][^=:\n]*\\)[ \t]*[=:][ \t]*\\(.*?\\)[ \t]*$")
             (let ((key (downcase (string-trim (match-string 1))))
                   (value (match-string 2)))
               (if pattern
@@ -197,12 +194,10 @@ If CONF is not found return nil."
                       top-props))))
 
            (t (error "Error while reading config file: %s:%d:\n    %s\n"
-                     conf current-line-number
+                     conf (line-number-at-pos)
                      (buffer-substring-no-properties (line-beginning-position)
                                                      (line-end-position)))))
-          (setq current-line-number (1+ current-line-number))
-          (goto-char (point-min))
-          (forward-line (1- current-line-number)))
+          (forward-line 1))
         (when pattern
           (push (make-editorconfig-core-handle-section
                  :name pattern

lisp/editorconfig.el

@@ -658,6 +658,10 @@ F is that function, and FILENAME and ARGS are arguments passed to F."
   "Return the coding system to use according to EditorConfig.
 Meant to be used on `auto-coding-functions'."
   (defvar auto-coding-file-name) ;; Emacs≥30
+  ;; Not only we don't want that an error in the `.editorconfig' file
+  ;; prevents opening a file but we don't want an error to be dropped on
+  ;; the floor by some `ignore-errors' higher up.
+  (with-demoted-errors "EditorConfig: %S"
     (when (and (stringp auto-coding-file-name)
                (file-name-absolute-p auto-coding-file-name)
 	       ;; Don't recurse infinitely.
@@ -668,7 +672,7 @@ Meant to be used on `auto-coding-functions'."
              (props (editorconfig-call-get-properties-function
                      auto-coding-file-name)))
         (editorconfig-merge-coding-systems (gethash 'end_of_line props)
-                                         (gethash 'charset props)))))
+                                           (gethash 'charset props))))))
 
 (defun editorconfig--get-dir-local-variables ()
   "Return the directory local variables specified via EditorConfig.