[DLTP-45176] Add complex compatibility in static mode for stft api.

python/paddle/signal.py

@@ -508,7 +508,10 @@ def istft(x,
         assert len(window.shape) == 1 and len(window) == win_length, \
             'expected a 1D window tensor of size equal to win_length({}), but got window with shape {}.'.format(win_length, window.shape)
     else:
-        window = paddle.ones(shape=(win_length, ))
+        window_dtype = paddle.float32 if x.dtype in [
+            paddle.float32, paddle.complex64
+        ] else paddle.float64
+        window = paddle.ones(shape=(win_length, ), dtype=window_dtype)
 
     if win_length < n_fft:
         pad_left = (n_fft - win_length) // 2
@@ -536,11 +539,10 @@ def istft(x,
             x = x[:, :, :n_fft // 2 + 1]
         out = fft_c2r(x=x, n=None, axis=-1, norm=norm, forward=False, name=None)
 
+    out = paddle.multiply(out, window).transpose(
+        perm=[0, 2, 1])  # (batch, n_fft, num_frames)
     out = overlap_add(
-        x=paddle.multiply(out, window).transpose(
-            perm=[0, 2, 1]),  # (batch, n_fft, num_frames)
-        hop_length=hop_length,
-        axis=-1)  # (batch, seq_length)
+        x=out, hop_length=hop_length, axis=-1)  # (batch, seq_length)
 
     window_envelop = overlap_add(
         x=paddle.tile(