patch 8.1.1414: alloc() returning "char_u *" causes a lot of type casts

Problem:    Alloc() returning "char_u *" causes a lot of type casts.
Solution:   Have it return "void *". (Mike Williams)  Define ALLOC_ONE() to
            check the simple allocations.
diff --git a/src/crypt_zip.c b/src/crypt_zip.c
index 25b7962..ec8c16e 100644
--- a/src/crypt_zip.c
+++ b/src/crypt_zip.c
@@ -90,7 +90,7 @@
     char_u	*p;
     zip_state_T	*zs;
 
-    zs = (zip_state_T *)alloc(sizeof(zip_state_T));
+    zs = ALLOC_ONE(zip_state_T);
     if (zs == NULL)
 	return FAIL;
     state->method_state = zs;