small change for tau

Author: jprhyne

SRC/dlarf1f.f

@@ -159,6 +159,9 @@ SUBROUTINE DLARF1F( SIDE, M, N, V, INCV, TAU, C, LDC, WORK )
       APPLYLEFT = LSAME( SIDE, 'L' )
       LASTV = 0
       LASTC = 0
+      IF( TAU.EQ.ZERO ) THEN
+         RETURN
+      END IF
       IF( TAU.NE.ZERO ) THEN
 !     Set up variables for scanning V.  LASTV begins pointing to the end
 !     of V.