Fix build with pyqt but no opengl

Signed-off-by: falkTX <falktx@falktx.com>

source/plugin/Makefile

@@ -155,6 +155,7 @@ TARGETS += \
 endif
 
 ifneq ($(HAIKU),true)
+ifeq ($(HAVE_DGL),true)
 ifeq ($(HAVE_PYQT),true)
 TARGETS += \
 	$(BINDIR)/CarlaRack$(LIB_EXT) \
@@ -168,6 +169,7 @@ TARGETS += \
 	$(BINDIR)/CarlaVstFxShell$(LIB_EXT)
 endif
 endif
+endif
 
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