scipy.signal.bspline does not work for integer types

scipy.signal.bspline gives zero output for integer types. This also affects quadratic and cubic.

Reproducing code example:

An example of an incorrect result

>>> from scipy.signal import bspline, quadratic, cubic
>>> bspline(np.array([-3,-2,-1,0,1,2,3]), 6)
array([0, 0, 0, 0, 0, 0, 0])

What was expected

>>> bspline(np.array([-3,-2,-1,0,1,2,3]).astype(float), 6)
array([2.17013889e-05, 1.56684028e-02, 2.28797743e-01, 5.11024306e-01,
       2.28797743e-01, 1.56684028e-02, 2.17013889e-05])

Scipy/Numpy/Python version information:

>>> import sys, scipy, numpy; print(scipy.__version__, numpy.__version__, sys.version_info)
1.7.0 1.21.1 sys.version_info(major=3, minor=7, micro=5, releaselevel='final', serial=0)

[poldap]

The PR is ready for you @tupui

[tupui]

@Dbhardwaj99 please read my comments.