patch 8.1.0370: not using internal diff if 'diffopt' is not changed

Problem:    Not using internal diff if 'diffopt' is not changed.
Solution:   Correct initialization of diff_flags. (Christian Brabandt)

src/diff.c

@@ -31,7 +31,7 @@ static int	diff_busy = FALSE;	/* ex_diffgetput() is busy */
 #define DIFF_VERTICAL	16	// vertical splits
 #define DIFF_HIDDEN_OFF	32	// diffoff when hidden
 #define DIFF_INTERNAL	64	// use internal xdiff algorithm
-static int	diff_flags = DIFF_FILLER;
+static int	diff_flags = DIFF_INTERNAL | DIFF_FILLER;
 
 static long diff_algorithm = 0;
 

src/version.c

@@ -794,6 +794,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    370,
 /**/
     369,
 /**/