Fix minor issues found by Clang's analysis.

Thanks to Denis Denisov for running the analysis.

Change-Id: I80810261e013423e746fd8d8afefb3581cffccc0
Reviewed-on: https://boringssl-review.googlesource.com/1701
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/crypto/evp/example_sign.c b/crypto/evp/example_sign.c
index 847330d..9d2a296 100644
--- a/crypto/evp/example_sign.c
+++ b/crypto/evp/example_sign.c
@@ -127,9 +127,13 @@
     fprintf(stderr, "sig_len mismatch\n");
     goto out;
   }
+
   sig = malloc(sig_len);
-  if (sig == NULL ||
-      EVP_DigestSignFinal(&md_ctx, sig, &sig_len) != 1) {
+  if (sig == NULL) {
+    goto out;
+  }
+  if (EVP_DigestSignFinal(&md_ctx, sig, &sig_len) != 1) {
+    free(sig);
     goto out;
   }