Fix conversion warning in xrepeat

[bredej]

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Description

The internal type of std::accumulate is determined by the init parameter.
Initializing with 0 (int) results in a "conversion from 'size_t' to 'type', possible loss of data" warning in MSVC.
Here is a link showcasing the warning in Compiler Explorer.

[tdegeus]

Thanks! Though are you actually initialising to zero?

[bredej]

From Zero-initialization on cppreference.com:
* If T is a scalar type, the object is initialized to the value obtained by explicitly converting the integer literal ​0​ (zero) to T.

Or to be explicit about the init value
shape_value_type{0}

[tdegeus]

Let's do it explicitly for readability. Also shape_value_type(0) is equally permitted right (which I personally find more readable, avoiding any suggestion of an array.

[bredej]

@tdegeus I have made the change you suggested.

[tdegeus]

Thanks