gl4: fix nullptr dereference in GL4Shader::CompileProgram
gl4: fix nullptr dereference in GL4Shader::CompileProgram

A nullptr dereference will occur when the disassembly string is not
found, which will obviously happen on AMD. Check for the condition and
if it is not found, put a message indicating so.

Rhodan81/xenia,sabretooth/xenia,wrren/xenia,MorganBauer/xenia,Rhodan81/xenia,toxic88/xenia,pwz3n0/xenia,bowlofstew/xenia,maxton/xenia,galek/xenia,KitoHo/xenia,DaTrollMon/xenia,MorganBauer/xenia,sephiroth99/xenia,herman-rogers/xenia,AbaiQi/xenia,DaTrollMon/xenia,bradparks/xenia__xbox_emulator,galek/xenia,bowlofstew/xenia,maxton/xenia,Drooids/xenia,greg100795/xenia,TingPing/xenia,bradparks/xenia__xbox_emulator,Rhodan81/xenia,toxic88/xenia,Drooids/xenia,no1dead/xenia,herman-rogers/xenia,wrren/xenia,ObsidianGuardian/xenia,sabretooth/xenia,TingPing/xenia,AbaiQi/xenia,greg100795/xenia,DaTrollMon/xenia,TingPing/xenia,no1dead/xenia,KitoHo/xenia,Drooids/xenia,herman-rogers/xenia,galek/xenia,TRex22/xenia,galek/xenia,no1dead/xenia,DaTrollMon/xenia,bowlofstew/xenia,sabretooth/xenia,pwz3n0/xenia,toxic88/xenia,bradparks/xenia__xbox_emulator,sephiroth99/xenia,greg100795/xenia,KitoHo/xenia,pwz3n0/xenia,no1dead/xenia,wrren/xenia,AbaiQi/xenia,greg100795/xenia,toxic88/xenia,ObsidianGuardian/xenia,AbaiQi/xenia,KitoHo/xenia,Drooids/xenia,MorganBauer/xenia,TRex22/xenia,herman-rogers/xenia,MorganBauer/xenia,pwz3n0/xenia,maxton/xenia,TingPing/xenia,sephiroth99/xenia,ObsidianGuardian/xenia,bradparks/xenia__xbox_emulator,wrren/xenia,Rhodan81/xenia,TRex22/xenia,bowlofstew/xenia