[Qemu-trivial] [PATCH] opts: fix NULL pointer derefernce in get_opt_value

[Mike Krinkin <krinkin.m.u@gmail.com>]

The value argument can be NULL, for example, in hw/i386/multiboot.c
in the load_multiboot function get_opt_value is explicitly called
with NULL as the second argument.

The problem was introduced in commit 950c4e6c94b1 ("opts: don't
silently truncate long option values"). This change fixes the
problem by adding a check whether the value is NULL or not.

Signed-off-by: Mike Krinkin <krinkin.m.u@gmail.com>
---
 util/qemu-option.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/util/qemu-option.c b/util/qemu-option.c
index 19761e3eaf..834217fc75 100644
--- a/util/qemu-option.c
+++ b/util/qemu-option.c
@@ -75,7 +75,9 @@ const char *get_opt_value(const char *p, char **value)
     size_t capacity = 0, length;
     const char *offset;
 
-    *value = NULL;
+    if (value) {
+        *value = NULL;
+    }
     while (1) {
         offset = qemu_strchrnul(p, ',');
         length = offset - p;
-- 
2.17.1