Fix uninitialized variable warnings.

gcc 6 displays these when compiling in release mode; all of these
warnings except the rankOk one were benign because there would have
been an error about the incomplete switch statement.

The rankOk warning highlighted a real problem: bailing early to
didnt_converge would have branched on an uninitialized variable.

src/generate.cpp

@@ -142,7 +142,7 @@ bool SolveSpaceUI::PruneConstraints(hGroup hg) {
 }
 
 void SolveSpaceUI::GenerateAll(Generate type, bool andFindFree, bool genForBBox) {
-    int first, last, i, j;
+    int first = 0, last = 0, i, j;
 
     uint64_t startMillis = GetMilliseconds(),
              endMillis;
@@ -355,7 +355,7 @@ void SolveSpaceUI::GenerateAll(Generate type, bool andFindFree, bool genForBBox)
     endMillis = GetMilliseconds();
 
     if(endMillis - startMillis > 30) {
-        const char *typeStr;
+        const char *typeStr = "";
         switch(type) {
             case Generate::DIRTY:           typeStr = "DIRTY";        break;
             case Generate::ALL:             typeStr = "ALL";          break;

src/render/rendergl1.cpp

@@ -308,7 +308,7 @@ void OpenGl1Renderer::SelectTexture(std::shared_ptr<const Pixmap> pm) {
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,     GL_CLAMP);
     glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
 
-    GLenum format;
+    GLenum format = 0;
     switch(pm->format) {
         case Pixmap::Format::RGBA: format = GL_RGBA;  break;
         case Pixmap::Format::RGB:  format = GL_RGB;   break;

src/request.cpp

@@ -81,7 +81,7 @@ void Request::Generate(IdList<Entity,hEntity> *entity,
                        IdList<Param,hParam> *param)
 {
     int points = 0;
-    Entity::Type et;
+    Entity::Type et = (Entity::Type)0;
     bool hasNormal = false;
     bool hasDistance = false;
     int i;
@@ -190,7 +190,7 @@ void Request::Generate(IdList<Entity,hEntity> *entity,
 }
 
 std::string Request::DescriptionString() const {
-    const char *s;
+    const char *s = "";
     if(h.v == Request::HREQUEST_REFERENCE_XY.v) {
         s = "#XY";
     } else if(h.v == Request::HREQUEST_REFERENCE_YZ.v) {

src/resource.cpp

@@ -264,8 +264,8 @@ std::shared_ptr<Pixmap> Pixmap::ReadPng(const std::string &filename, bool flip)
 }
 
 bool Pixmap::WritePng(FILE *f, bool flip) {
-    int colorType;
-    bool bgr;
+    int colorType = 0;
+    bool bgr = false;
     switch(format) {
         case Format::RGBA: colorType = PNG_COLOR_TYPE_RGBA; bgr = false; break;
         case Format::BGRA: colorType = PNG_COLOR_TYPE_RGBA; bgr = true;  break;

src/system.cpp

@@ -440,6 +440,9 @@ SolveResult System::Solve(Group *g, int *dof, List<hConstraint> *bad,
         p->tag = alone;
         WriteJacobian(alone);
         if(!NewtonSolve(alone)) {
+            // We don't do the rank test, so let's arbitrarily return
+            // the DIDNT_CONVERGE result here.
+            rankOk = true;
             // Failed to converge, bail out early
             goto didnt_converge;
         }