patch 8.0.1307: compiler warning for ignoring return value

Problem:    Compiler warning for ignoring return value of ftruncate(). (Tony
            Mechelynck)
Solution:   Assign returned value to "ignore".
diff --git a/src/fileio.c b/src/fileio.c
index e76e3d1..2c5c8b9 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4517,7 +4517,7 @@
 #endif
 #ifdef HAVE_FTRUNCATE
 	    if (!append)
-		ftruncate(fd, (off_t)0);
+		ignored = ftruncate(fd, (off_t)0);
 #endif
 
 #if defined(WIN3264)