`pddbtrf` emmits unecessary warning due to trivial lead

[TLCFEM]

GEMM and GEMV require lead to be positive.

A zero lead emmits the following message.

 ** On entry to DGEMV  parameter number  6 had an illegal value

The following calls do not safeguard MAX_BW, BWL or BWU which could be zero.

scalapack/SRC/pddbtrf.f

Lines 764 to 767 in a23c2cd

	CALL DGEMM( 'T', 'N', MAX_BW, MAX_BW, MAX_BW, -ONE,
	$ AF( ODD_SIZE*BWU+2*MBW2+1 ), MAX_BW,
	$ AF( WORK_U+ODD_SIZE*BWL+2*MBW2+1 ), MAX_BW, ONE,
	$ A( OFST+ODD_SIZE*LLDA+1+BWU ), LLDA-1 )

scalapack/SRC/pddbtrf.f

Lines 842 to 845 in a23c2cd

	CALL DGEMM( 'N', 'T', BWU, BWL, ODD_SIZE, -ONE, AF( 1 ),
	$ BWU, AF( WORK_U+1 ), BWL, ZERO,
	$ AF( 1+MAX( 0, BWL-BWU )+ODD_SIZE*BWU+( 2*MAX_BW+
	$ MAX( 0, BWU-BWL ) )*MAX_BW ), MAX_BW )

scalapack/SRC/pddbtrf.f

Lines 806 to 809 in a23c2cd

	CALL DGEMV( 'N', BWL, I2, -ONE,
	$ AF( WORK_U+1+( I1-1-I2 )*BWL ), BWL,
	$ A( OFST+BWU+1+I2+( I1-1-I2 )*LLDA ), LLDA-1,
	$ ONE, AF( WORK_U+1+( I1-1 )*BWL ), 1 )

scalapack/SRC/pddbtrf.f

Lines 823 to 825 in a23c2cd

	CALL DGEMV( 'N', BWU, I2, -ONE, AF( ( I1-1-I2 )*BWU+1 ),
	$ BWU, A( OFST+BWU+1-I2+( I1-1 )*LLDA ), 1,
	$ ONE, AF( ( I1-1 )*BWU+1 ), 1 )