Ensure result of ftell is checked for errors

The ftell call in the html renderer handling of drag and drop was not
checking its return value for errors which could have resulted in
attempting to read -1 bytes.

coverity 1251038

1 files changed, 6 insertions, 0 deletions

diff --git a/render/html.c b/render/html.c
index 5fb2feabd..e8692a0a7 100644
--- a/render/html.c
+++ b/render/html.c
@@ -1934,6 +1934,12 @@ static bool html_drop_file_at_point(struct content *c, int x, int y, char *file)
 		file_len = ftell(fp);
 		fseek(fp, 0, SEEK_SET);
 
+		if ((long)file_len == -1) {
+			/* unable to get file length, but drop was for us */
+			fclose(fp);
+			return true;
+		}
+
 		/* Allocate buffer for file data */
 		buffer = malloc(file_len + 1);
 		if (buffer == NULL) {