patch 8.0.0307: asan detects a memory error when EXITFREE is defined

Problem:    Asan detects a memory error when EXITFREE is defined. (Dominique
            Pelle)
Solution:   In getvcol() check for ml_get_buf() returning an empty string.
            Also skip adjusting the scroll position.  Set "exiting" in
            mch_exit() for all systems.

src/charset.c

@@ -1296,6 +1296,10 @@ getvcol(
 	posptr = NULL;  /* continue until the NUL */
     else
     {
+	/* Special check for an empty line, which can happen on exit, when
+	 * ml_get_buf() always returns an empty string. */
+	if (*ptr == NUL)
+	    pos->col = 0;
 	posptr = ptr + pos->col;
 #ifdef FEAT_MBYTE
 	if (has_mbyte)

src/os_amiga.c

@@ -889,6 +889,8 @@ mch_early_init(void)
     void
 mch_exit(int r)
 {
+    exiting = TRUE;
+
     if (raw_in)			    /* put terminal in 'normal' mode */
     {
 	settmode(TMODE_COOK);

src/os_mswin.c

@@ -201,6 +201,8 @@ int _stricoll(char *a, char *b)
     void
 mch_exit(int r)
 {
+    exiting = TRUE;
+
     display_errors();
 
     ml_close_all(TRUE);		/* remove all memfiles */

src/os_win32.c

@@ -2538,8 +2538,9 @@ mch_init(void)
     void
 mch_exit(int r)
 {
-    stoptermcap();
+    exiting = TRUE;
 
+    stoptermcap();
     if (g_fWindInitCalled)
 	settmode(TMODE_COOK);
 

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    307,
 /**/
     306,
 /**/

src/window.c

@@ -5708,7 +5708,10 @@ win_new_height(win_T *wp, int height)
     wp->w_height = height;
     wp->w_skipcol = 0;
 
-    scroll_to_fraction(wp, prev_height);
+    /* There is no point in adjusting the scroll position when exiting.  Some
+     * values might be invalid. */
+    if (!exiting)
+	scroll_to_fraction(wp, prev_height);
 }
 
     void