rs690: fix r300 swtcl bug in DMA code.
rs690: fix r300 swtcl bug in DMA code.

When we finish emitting swtcl objects, we request space in the cmdbuf,
and flush if no space exists. However in this case we also flush
the DMA buffer we just put the vertices we wanted to send in.

This checks in advance if we have space in the buffer.

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