Allow 0-byte files in full OTAs.

Currently, the writeProcessFunction fails when
there are zero bytes to write, potentially returning
errno from a previous operation, or hanging
indefinitely while it waits for a >0 result on a
write of size 0.  This happens when the output
file is intended to be zero bytes in size.

Change-Id: Ib3cfcaf66d82942bc89e5f5c64697862403b38da

minzip/Zip.c

@@ -698,7 +698,9 @@ static bool writeProcessFunction(const unsigned char *data, int dataLen,
                                  void *cookie)
 {
     int fd = (int)(intptr_t)cookie;
-
+    if (dataLen == 0) {
+        return true;
+    }
     ssize_t soFar = 0;
     while (true) {
         ssize_t n = write(fd, data+soFar, dataLen-soFar);