Unicode strings are displayed incorrectly in output for MIPS

I have a MIPS PE executable for Windows CE6.
IDA7 correctly displays references to Unicode strings and their contents.
But, decompilation output of Retdec is unreadable. For example, IDA7:
```lui $t1, %hi(aMgrtskChangede) # "MgrTsk_ChangeDebugLevel"
lui $t2, %hi(aApplinkS) # "[AppLink] %s: "
addiu $a1, $t1, %lo(aMgrtskChangede) # "MgrTsk_ChangeDebugLevel"
jal NKDbgPrintfW
addiu $a0, $t2, %lo(aApplinkS) # "[AppLink] %s: "
lui $a0, %hi(aFailInvalidInp) # "fail, invalid input\r\n"
jal NKDbgPrintfW
la $a0, %lo(aFailInvalidInp) # "fail, invalid input\r\n"
```

Retdec output:

``` // 0x403dc
NKDbgPrintfW((int32_t)"[\x00\x41\x00p\x00p\x00L\x00i\x00n\x00k", (int32_t)"C\x00S\x00y\x00s\x00t\x00\x65\x00m\x00\x45\x00n\x00v\x00:\x00:\x00R");
int32_t v5 = v1 + 1; // 0x403f0
NKDbgPrintfW((int32_t)"S\x00M\x00\x41\x00R\x00T\x00P\x00H\x00O\x00N\x00\x45\x00_\x00L\x00I\x00N\x00K\x00_\x00\x41\x00P", v5);
```

I tried changing `NKDbgPrintfW` prototype, but that didn't help. Also, VA arguments and their count are wrong, I'll probably file a separate issue about that.

No source file or test is named. Start by reproducing the issue with the supplied MIPS PE executable and trace how RetDec decodes and prints Unicode string references in decompilation output, comparing the result with IDA7; done means readable Unicode strings are emitted and the existing prototype change is no longer needed.

Written by the indexing model from the issue text.