"""Processes a string containing LaTeX square root expressions to ensure proper curly brace formatting.

This function scans the input string for LaTeX square root expressions (`\\sqrt`). If any `\\sqrt` expressions are found, it ensures that the argument of the square root is enclosed in curly braces. If the argument is not already enclosed in braces, the function adds them.

Args:
    string (str): The input string containing LaTeX square root expressions.

Returns:
    str: The processed string with all `\\sqrt` expressions properly formatted with curly braces.

Examples:
    >>> _fix_sqrt('\\sqrt{a}')
    '\\sqrt{a}'
    >>> _fix_sqrt('\\sqrta')
    '\\sqrt{a}'
    >>> _fix_sqrt('\\sqrt{a} + \\sqrtb + \\sqrt{c}')
    '\\sqrt{a} + \\sqrt{b} + \\sqrt{c}'
    >>> _fix_sqrt('x + \\sqrt{y} + z + \\sqrt{w}')
    'x + \\sqrt{y} + z + \\sqrt{w}'
"""