Fix string-distance for two empty strings

* fns.c (Fstring_distance): Avoid using uninitialized memory.
* test/src/fns-tests.el (test-string-distance): Add test cases.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/fns.c b/src/fns.c
index 4e74589ef26..a72e41aee5b 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -322,7 +322,7 @@ Letter-case is significant, but text properties are ignored. */)
 
   USE_SAFE_ALLOCA;
   ptrdiff_t *column = SAFE_ALLOCA ((len1 + 1) * sizeof (ptrdiff_t));
-  for (y = 1; y <= len1; y++)
+  for (y = 0; y <= len1; y++)
     column[y] = y;
 
   if (use_byte_compare)