examples: check asprintf return value in client_info.c

On error, asprintf returns -1 and the contents of the string
pointer is undefined. In the rest of the libvirt code,
the virAsprintf wrapper takes care of that.

Check the return value and report a generic error, since we
purposefully avoid linking to virutil.

examples/admin/client_info.c

@@ -86,6 +86,11 @@ exampleGetTypedParamValue(virTypedParameterPtr item)
         return NULL;
     }
 
+    if (ret < 0) {
+        fprintf(stderr, "error formatting typed param value\n");
+        return NULL;
+    }
+
     return str;
 }