Use a uniform approach for the largest value of an unsigned type.

compress.c

@@ -28,7 +28,7 @@ int ZEXPORT compress2 (dest, destLen, source, sourceLen, level)
 {
     z_stream stream;
     int err;
-    const uInt max = (uInt)0 - 1;
+    const uInt max = (uInt)-1;
     uLong left;
 
     left = *destLen;

inflate.c

@@ -1555,7 +1555,7 @@ unsigned long ZEXPORT inflateCodesUsed(strm)
 z_streamp strm;
 {
     struct inflate_state FAR *state;
-    if (inflateStateCheck(strm)) return (unsigned long)0 - 1;
+    if (inflateStateCheck(strm)) return (unsigned long)-1;
     state = (struct inflate_state FAR *)strm->state;
     return (unsigned long)(state->next - state->codes);
 }

uncompr.c

@@ -32,7 +32,7 @@ int ZEXPORT uncompress2 (dest, destLen, source, sourceLen)
 {
     z_stream stream;
     int err;
-    const uInt max = (uInt)0 - 1;
+    const uInt max = (uInt)-1;
     uLong len, left;
     Byte buf[1];    /* for detection of incomplete stream when *destLen == 0 */