Replace log with select for generating the attention mask to avoid NaNs on zero values.

zml/nn.zig

@@ -699,12 +699,16 @@ pub fn causalAttnMask(
             mask = mask.logical(.AND, window_mask);
         }
     }
-    mask = mask.convert(dtype);
+
     if (dtype.isFloat()) {
-        // use log to convert "true" (ie 1) to 0, and "false" (ie 0) to -inf
         meta.guard(dtype.isFloat(), @src()); // -inf only exists for floats
-        mask = mask.log();
+        const zeros = Tensor.constant(mask.shape(), dtype.zero());
+        const minus_inf = Tensor.constant(mask.shape(), dtype.minValue());
+        mask = Tensor.select(mask, zeros, minus_inf);
+    } else {
+        mask = mask.convert(dtype);
     }
+
     return mask;
 }