FEXLoader/ELFCodeLoader: Be robust against zero length environment va…

…riables

For some reason steamwebhelper is setting a zero length environment
variable. This was causing an assert to be raised early as the web
helper was starting up.

Just stop trying to memcpy the zero length string, gets steamwebhelper
working in the steam beta client again

Source/Tools/FEXLoader/ELFCodeLoader.h

@@ -655,7 +655,7 @@ class ELFCodeLoader final : public FEX::CodeLoader {
       }
 
       // Set the null terminator for the string
-      *reinterpret_cast<uint8_t*>(ArgumentBackingBase + CurrentOffset + ArgSize + 1) = 0;
+      *reinterpret_cast<uint8_t*>(ArgumentBackingBase + CurrentOffset + ArgSize) = 0;
 
       CurrentOffset += ArgSize + 1;
     }
@@ -667,10 +667,12 @@ class ELFCodeLoader final : public FEX::CodeLoader {
       EnvpPointers[i] = EnvpBackingBaseGuest + CurrentOffset;
 
       // Copy the string in to the final location
-      memcpy(reinterpret_cast<void*>(EnvpBackingBase + CurrentOffset), &EnvironmentVariables[i].at(0), EnvpSize);
+      if (EnvpSize) {
+        memcpy(reinterpret_cast<void*>(EnvpBackingBase + CurrentOffset), &EnvironmentVariables[i].at(0), EnvpSize);
+      }
 
       // Set the null terminator for the string
-      *reinterpret_cast<uint8_t*>(EnvpBackingBase + CurrentOffset + EnvpSize + 1) = 0;
+      *reinterpret_cast<uint8_t*>(EnvpBackingBase + CurrentOffset + EnvpSize) = 0;
 
       CurrentOffset += EnvpSize + 1;
     }