Fix a GCC compiler warning. The type of the second argument of memset is int, not float.
Fix code using 'false' as return value where type 'const SpellEntry*' is expected.
Fix a bunch of GCC compiler warnings about missing field initializers [-Wmissing-field-initializers].
Fix code to prevent narrowing when {} initializing, which is ill-formed in recent C++ standards!

The values for the texts to yell are negative, so it's better to use signed integers, and even more so if the values are only used to pass to DoScriptText(), whose first argument is also of type int32.