Fix memory allocation for wpe_pasteboard_string

The "data" member of wpe_pasteboard_string is a dynamically allocated
array of characters, and allocated size must be "sizeof(char) * in_length".
Also, calloc() already computes the final size itself, so pass the
"in_length" parameter as the number of elements, and "sizeof(char)" as
the element size.

Author: aperezdc

src/pasteboard.c

@@ -36,7 +36,7 @@ wpe_pasteboard_string_initialize(struct wpe_pasteboard_string* string, const cha
     if (string->data)
         return;
 
-    string->data = calloc(1, sizeof(char*) * in_length);
+    string->data = calloc(in_length, sizeof(char));
     string->length = in_length;
     memcpy(string->data, in_string, in_length);
 }