glsl2: Early return with visit_continue in loop_analysis::visit(ir_dereference_variable *)
glsl2: Early return with visit_continue in loop_analysis::visit(ir_dereference_variable *)

Returning early with visit_continue_with_parent prevented the
then-statements and else-statements of if-statements such as the
following from being processed:

	  if (some_var) { ... } else { ... }

Fixes piglit test case glsl-fs-loop-nested-if and bugzilla #30030.

adobe/glsl2agal,adobe/glsl2agal,tokyovigilante/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,zeux/glsl-optimizer,mapbox/glsl-optimizer,benaadams/glsl-optimizer,tokyovigilante/glsl-optimizer,mapbox/glsl-optimizer,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,zz85/glsl-optimizer,mcanthony/glsl-optimizer,zeux/glsl-optimizer,mcanthony/glsl-optimizer,dellis1972/glsl-optimizer,KTXSoftware/glsl2agal,jbarczak/glsl-optimizer,djreep81/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,mapbox/glsl-optimizer,KTXSoftware/glsl2agal,dellis1972/glsl-optimizer,tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,adobe/glsl2agal,benaadams/glsl-optimizer,zz85/glsl-optimizer,zeux/glsl-optimizer,adobe/glsl2agal,bkaradzic/glsl-optimizer,wolf96/glsl-optimizer,KTXSoftware/glsl2agal,zz85/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,bkaradzic/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,metora/MesaGLSLCompiler,djreep81/glsl-optimizer,metora/MesaGLSLCompiler,wolf96/glsl-optimizer,zz85/glsl-optimizer,benaadams/glsl-optimizer,KTXSoftware/glsl2agal,benaadams/glsl-optimizer,KTXSoftware/glsl2agal,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,dellis1972/glsl-optimizer,benaadams/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,metora/MesaGLSLCompiler,zz85/glsl-optimizer,adobe/glsl2agal,jbarczak/glsl-optimizer,mapbox/glsl-optimizer