Fix compilation warnings in ZLib (MSVC)

Yes, we are changing the Zlib code. This is dangerous and uncool.
Fortunately, these are just some implicit casts.

deps/zlib/deflate.h

@@ -317,15 +317,15 @@ void ZLIB_INTERNAL _tr_stored_block OF((deflate_state *s, charf *buf,
 #endif
 
 # define _tr_tally_lit(s, c, flush) \
-  { uch cc = (c); \
+  { uch cc = (uch)(c); \
     s->d_buf[s->last_lit] = 0; \
     s->l_buf[s->last_lit++] = cc; \
     s->dyn_ltree[cc].Freq++; \
     flush = (s->last_lit == s->lit_bufsize-1); \
    }
 # define _tr_tally_dist(s, distance, length, flush) \
-  { uch len = (length); \
-    ush dist = (distance); \
+  { uch len = (uch)(length); \
+    ush dist = (ush)(distance); \
     s->d_buf[s->last_lit] = dist; \
     s->l_buf[s->last_lit++] = len; \
     dist--; \

deps/zlib/trees.c

@@ -605,7 +605,7 @@ local void gen_codes (tree, max_code, bl_count)
         int len = tree[n].Len;
         if (len == 0) continue;
         /* Now reverse the bits */
-        tree[n].Code = bi_reverse(next_code[len]++, len);
+        tree[n].Code = (ush)bi_reverse(next_code[len]++, len);
 
         Tracecv(tree != static_ltree, (stderr,"\nn %3d %c l %2d c %4x (%x) ",
              n, (isgraph(n) ? n : ' '), len, tree[n].Code, next_code[len]-1));
@@ -729,7 +729,7 @@ local void scan_tree (s, tree, max_code)
         if (++count < max_count && curlen == nextlen) {
             continue;
         } else if (count < min_count) {
-            s->bl_tree[curlen].Freq += count;
+            s->bl_tree[curlen].Freq += (ush)count;
         } else if (curlen != 0) {
             if (curlen != prevlen) s->bl_tree[curlen].Freq++;
             s->bl_tree[REP_3_6].Freq++;