mu4e: don't change context at startup when there is one

Since people often go start/stop mu4e, we shouldn't try to pick a
default context if one is already set.

mu4e/mu4e-compose.el

@@ -127,7 +127,8 @@ If POLICY is
 
 In all other cases, if any context matches (using its match
 function), this context is returned. If none of the contexts
-match, POLICY determines what to do:
+match, and if there is no current context, POLICY determines what
+to do:
 
 - pick-first: pick the first of the contexts available
 - ask: ask the user

mu4e/mu4e-context.el

@@ -130,7 +130,8 @@ POLICY specifies how to do the determination. If POLICY is
 
 In all other cases, if any context matches (using its match
 function), this context is returned. If none of the contexts
-match, POLICY determines what to do:
+match, and if there is no current context, POLICY determines what
+to do:
 
 - pick-first: pick the first of the contexts available
 - ask: ask the user
@@ -138,11 +139,14 @@ match, POLICY determines what to do:
   (when mu4e-contexts
     (if (eq policy 'always-ask)
       (mu4e~context-ask-user "Select context: ")
-      (or (find-if (lambda (context)
+      (or ;; is there a matching one?
+	(find-if (lambda (context)
 		     (and (mu4e-context-match-func context)
 		       (funcall (mu4e-context-match-func context) msg)))
-	    mu4e-contexts)
-	;; no context found
+	  mu4e-contexts)
+	;; no matching one; but is there a current one?
+	(mu4e-context-current) 	
+	;; no context found yet; consult policy
 	(case policy
 	  (pick-first (car mu4e-contexts))
 	  (ask (mu4e~context-ask-user "Select context: "))

mu4e/mu4e-utils.el

@@ -97,9 +97,9 @@ User's addresses are set in `mu4e-user-mail-address-list')."
   (declare (indent 2))
   `(let* ((vars (and ,context (mu4e-context-vars ,context))))
      (progv ;; XXX: perhaps use eval's lexical environment instead of progv?
-      (mapcar (lambda(cell) (car cell)) vars)
-      (mapcar (lambda(cell) (cdr cell)) vars)
-      (eval ,@body))))
+       (mapcar (lambda(cell) (car cell)) vars)
+       (mapcar (lambda(cell) (cdr cell)) vars)
+       (eval ,@body))))
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; the standard folders can be functions too

mu4e/mu4e-vars.el

@@ -224,7 +224,8 @@ If POLICY is 'always-ask, we ask the user unconditionally.
 
 In all other cases, if any context matches (using its match
 function), this context is returned. If none of the contexts
-match, POLICY determines what to do:
+match, and if there is no current context, POLICY determines what
+to do:
 
 - pick-first: pick the first of the contexts available
 - ask: ask the user