patch 8.0.0497: arabic support is not fully tested

Problem:    Arabic support is not fully tested.
Solution:   Add more tests for the untested functions.  Comment out
            unreachable code.
diff --git a/src/arabic.c b/src/arabic.c
index cb43b80..9bc1669 100644
--- a/src/arabic.c
+++ b/src/arabic.c
@@ -24,7 +24,9 @@
 static int  chg_c_a2i(int cur_c);
 static int  chg_c_a2m(int cur_c);
 static int  chg_c_a2f(int cur_c);
+#if 0
 static int  chg_c_i2m(int cur_c);
+#endif
 static int  chg_c_f2m(int cur_c);
 static int  chg_c_laa2i(int hid_c);
 static int  chg_c_laa2f(int hid_c);
@@ -418,7 +420,10 @@
 
 /*
  * Change shape - from Initial to Medial
+ * This code is unreachable, because for the relevant characters ARABIC_CHAR()
+ * is FALSE;
  */
+#if 0
     static int
 chg_c_i2m(int cur_c)
 {
@@ -450,6 +455,7 @@
     }
     return 0;
 }
+#endif
 
 
 /*
@@ -608,7 +614,11 @@
     else if (!shape_c || A_is_f(shape_c) || A_is_s(shape_c) || prev_laa)
 	curr_c = A_is_valid(next_c) ? chg_c_a2i(c) : chg_c_a2s(c);
     else if (A_is_valid(next_c))
+#if 0
 	curr_c = A_is_iso(c) ? chg_c_a2m(c) : chg_c_i2m(c);
+#else
+	curr_c = A_is_iso(c) ? chg_c_a2m(c) : 0;
+#endif
     else if (A_is_valid(prev_c))
 	curr_c = chg_c_a2f(c);
     else