Fix typos

Found via `codespell -q 3 -L aci,addmin,ake,aline,alle,alledges,alocation,als,ang,anid,anormal,aply,apoints,ba,beginn,behaviour,bloaded,bottome,brushin,bu,byteorder,calculater,cancelled,cancelling,cas,cascade,centimetre,childrens,childs,colour,colours,commen,connexion,currenty,documentin,dof,doubleclick,dum,eiter,elemente,ende,feld,finde,findf,findn,fle,freez,graphin,hist,iff,incrementin,indexin,indicies,initialisation,initialise,initialised,initialises,initialisiert,inout,ist,itsel,kilometre,leadin,localy,lod,mantatory,methode,metres,millimetre,modell,nd,noe,normale,normaly,nto,numer,oce,oder,ontop,orgin,orginx,orginy,ot,pard,parm,parms,pres,programm,que,rady,recurrance,renderin,rin,ro,rougly,sectionin,seperator,serie,shs,sinc,siz,som,strack,substraction,te,technic,thist,thru,tread,tru,ue,uint,unter,uptodate,vas,vertexes,vew,wallthickness,whitespaces -S "./.git,*.po,*.ts,*.pdf,./ChangeLog.txt,./src/3rdParty,./src/Mod/Assembly/App/opendcm,./src/CXX,./src/zipios++,./src/Base/swig*,./src/Mod/Robot/App/kdl_cp,./src/Mod/Import/App/SCL,./src/WindowsInstaller,./src/Doc/FreeCAD.uml,./src/Base/StackWalker.cpp,./build/doc/SourceDoc,./tools/build/WindowsInstaller/lang,./src/Mod/TechDraw/Templates/locale"`

src/Mod/Material/App/Exceptions.h

@@ -34,7 +34,7 @@ class Uninitialized: public Base::Exception
 {
 public:
     Uninitialized()
-        : Base::Exception("Uninitalized")
+        : Base::Exception("Uninitialized")
     {}
     explicit Uninitialized(const char* msg)
         : Base::Exception(msg)
@@ -244,7 +244,7 @@ class UnknownValueType: public Base::Exception
 {
 public:
     UnknownValueType()
-        : Base::Exception("Unkown value type")
+        : Base::Exception("Unknown value type")
     {}
     explicit UnknownValueType(const char* msg)
         : Base::Exception(msg)