Initialize variable for not-all-knowing-compilers

src/ziptool.c

diff --git a/src/ziptool.c b/src/ziptool.c
index 70e4508..2d68cb9 100644
--- a/src/ziptool.c
+++ b/src/ziptool.c
@@ -1064,7 +1064,7 @@
 main(int argc, char *argv[])
 {
     const char *archive;
-    zip_source_t *memory_src;
+    zip_source_t *memory_src = NULL;
     unsigned int i;
     int c, arg, err, flags;
     const char *prg;