flexfield validation for interval is not processed correctly
it is accepting symbols and numbers

when adding flexfield:

• it will refresh back to 0 if contains first symbol then numbers (example, "a123", "abc12x", "xz1")
• it will save only first numbers when entered numbers and then symbols (example, "123ab" will save "123"; "12ab56" will save "12"; "98abxc" will save "98")

this fix should apply to following forms:

• item form (templates and hosts)
• item prototype form (templates and hosts)
• discovery rule form (templates and hosts)