Fix: set proper size when creating new strings

After adding a wrapper to g_array_index that validates that accessed
indices don't go past the end of the arrays, I got this:

    (╯°□°)╯︵ ┻━┻  /home/smarchi/src/babeltrace/src/lib/trace-ir/field.c:392: create_string_field(): Assertion `0 < string_field->buf->len` failed.

The problem is that arrays backing string fields are created with:

    string->buf = g_array_sized_new(FALSE, FALSE, sizeof(char), 1);

This g_array_sized_new call reserves space for one element, but doesn't
actually make the length of the array one.  Add a call to
g_array_set_size to fix that.  Fix another occurence of the same bug in
ctf-writer.

Signed-off-by: Simon Marchi <[email protected]>
Signed-off-by: Philippe Proulx <[email protected]>
Change-Id: I147cdaaa7cff00ee06ec4c98bd9423a975ddd770

Author: simark

src/ctf-writer/fields.c

@@ -184,6 +184,7 @@ int bt_ctf_field_common_string_initialize(struct bt_ctf_field_common *field,
 		goto end;
 	}
 
+	g_array_set_size(string->buf, 1);
 	g_array_index(string->buf, char, 0) = '\0';
 	BT_LOGD("Initialized common string field object: addr=%p, ft-addr=%p",
 		field, type);

src/lib/trace-ir/field.c

@@ -398,6 +398,7 @@ struct bt_field *create_string_field(struct bt_field_class *fc)
 		goto end;
 	}
 
+	g_array_set_size(string_field->buf, 1);
 	g_array_index(string_field->buf, char, 0) = '\0';
 	BT_LIB_LOGD("Created string field object: %!+f", string_field);