[rtext] Check for empty strings in TextToPascal and TextToCamel

[Ne0nWinds]

Both TextToPascal and TextToCamel read past the end of empty strings (""). These are the only two text functions that don't handle this case.

In both functions, the main for loop skips over index 0 and starts directly at index 1. This also inadvertently skips over the null-terminator check for index 0.

Solution: add a simple text[0] != '\0' check before the main loop in each function.

[raysan5]

@Ne0nWinds please, could you add parenthesis to conditions, as per raylib code conentions, thanks

[raysan5]

@Ne0nWinds thanks for the review