vf_unsharp: set default chroma size value to 5x5

The previous default value 0x0 was not good, since it is not even
valid.

doc/filters.texi

@@ -1850,7 +1850,7 @@ It accepts the following parameters:
 
 Negative values for the amount will blur the input video, while positive
 values will sharpen. All parameters are optional and default to the
-equivalent of the string '5:5:1.0:0:0:0.0'.
+equivalent of the string '5:5:1.0:5:5:0.0'.
 
 @table @option
 
@@ -1868,11 +1868,11 @@ and 5.0, default value is 1.0.
 
 @item chroma_msize_x
 Set the chroma matrix horizontal size. It can be an integer between 3
-and 13, default value is 0.
+and 13, default value is 5.
 
 @item chroma_msize_y
 Set the chroma matrix vertical size. It can be an integer between 3
-and 13, default value is 0.
+and 13, default value is 5.
 
 @item chroma_amount
 Set the chroma effect strength. It can be a float number between -2.0

libavfilter/vf_unsharp.c

@@ -132,8 +132,8 @@ static void set_filter_param(FilterParam *fp, int msize_x, int msize_y, double a
 static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
 {
     UnsharpContext *unsharp = ctx->priv;
-    int lmsize_x = 5, cmsize_x = 0;
-    int lmsize_y = 5, cmsize_y = 0;
+    int lmsize_x = 5, cmsize_x = 5;
+    int lmsize_y = 5, cmsize_y = 5;
     double lamount = 1.0f, camount = 0.0f;
 
     if (args)