1011 - Unnamed modification must follow a variable assignment in the same scope.

Description
A variable modification operator was used without specifying the variable to append to. This is supported, provided the destination variable was previously referenced.
Example
Config:
+ 'String' // BAD - No variable to assign to
Output:
c:\Test\fbuild.bff(1):(7) FASTBuild Error #1011 - Unnamed modification must follow a variable assignment in the same scope. + 'String' ^ \--here
Fix:
.MyVar = 'hello' + 'String' // OK - The destination variable can be inferred